CHAPTER TWO KANT, SKEPTICISM, AND THE COMPARISON ARGUMENT ALBERTO VANZO IIntroduction1 The beginning of the section on truth in Immanuel Kant's Logic, the logic handbook compiled by Gottlob Benjamin Jäsche on Kant's behalf, outlines the comparison argument about truth.2 This is a famous argument, 1 In this paper, I cite the Logik Bauch, the Logik Hechsel, and the Warschauer Logik, which are not included in the Academy Edition. They are cited with the abbreviation "VLP", followed by the page number and, eventually, the line number of from Tillman Pinder's edition: Immanuel Kant, Logik-Vorlesung: Unveröffentliche Nachschriften (Hamburg: Meiner, 1998). Reflexionen and lecture transcripts raise several philological problems. See Elfriede Conrad, Kants Logikvorlesungen als neuer Schlüssel zur Architektonik der Kritik der reinen Vernunft: Die Ausarbeitung der Gliederungsentwürfe in den Logikvorlesungen als Auseinandersetzung mit der Tradition (Stuttgart: Frommann-Holzboog, 1994), 4365. In the light of those problems, when citing Reflexionen and lecture transcripts, I mostly rely on statements which can be found in more than one source: Reflexionen, or lecture transcripts, or Reflexionen and lecture transcripts alongside Kant's works and letters. I assume the following datings for the lectures on which the lecture transcripts used in this paper are based. Logik Dohna, Logik Pölitz, Metaphysik Dohna, Metaphysik L2, Wiener Logik, and the marginal annotations of Logik Bauch are based on lectures given from the early 1780s onwards. Philosophische Enziklopädie, Logik Hechsel, and Warschauer Logik are based on lectures given around 1780. Logik Busolt and the main text of Logik Bauch are based on lectures given in several different years, probably including pre-Critical materials. Anthropologie Collins, Logik Blomberg, and Logik Philippi are based on lectures given in the early 1770s. 2 I will mainly quote the exposition of the comparison argument in the Jäsche Logic. This is not a very reliable source of Kant's critical thought. See Terry Kant, Skepticism, and the Comparison Argument 55 which has been advanced by many thinkers throughout the history of philosophy: Sextus Empiricus, Frege, Bosanquet, Dewey, Hempel, Goodman, Putnam, Davidson, and BonJour, among others.3 The comparison argument goes along these lines: (a) According to the correspondence theory of truth, a truth-bearer p (such as a proposition, a sentence, or a judgment) is true if and only if it corresponds, or it agrees, with a portion of reality: typically, the object(s), state(s) of affairs, or event(s) p is about. To know whether p is true is to know whether p agrees with that portion of reality. (b) In order to know whether p agrees with that portion of reality, one must check if that portion of reality is as p states. Using the language of the comparison argument, one must compare p with that portion of reality. (c) To do this, one must have some reliable piece of information on that portion of reality (such as perceptions or judgments of perception). Comparing p with a portion of reality means checking whether p is supported by such a reliable piece of information. If it is, then one has a reason to believe that p is true. Boswell, "On the Textual Authenticity of Kant's Logic," History and Philosophy of Logic 9 (1988): 193-203. However, a transcript of lectures that Kant gave right after the completion of the first Critique illustrates the comparison argument in the same terms of Jäsche's handbook: VL 24:822. Transcripts of lectures given between 1777 and 1782 (VPE 24:2022-27; VLP 548) and in the 1770s (VL 24:81; VL 24:387 = VPE 76-77) outline the comparison argument. A sentence of the Critique of Pure Reason and a few of Kant's notes from the Critical time can be read in relation to the comparison argument (KrV A104; RL 2161 [1776-78? 17901804?], 16:255; RM 5642 [1780-83], 16:28118-27). Hence, despite the unreliability of the Jäsche Logic, there is no doubt that the comparison argument is part of Kant's Critical doctrines on truth. 3 For references, see Douglas McDermid, "Putnam on Kant on Truth: Correspondence or Coherence?" Idealistic Studies 28 (1998): 28 n. 29. Kant's most likely source of the comparison argument is Johann Heinrich Samuel Formey's entry "Dialéle" in Encyclopédie, ou Dictionnaire raisonné des sciences, des arts et des métiers, eds. Denis Diderot and Jean D'Alembert (Paris, 1751-77), vol. 4, 935. This entry explains what a diallelus is by employing the same example that is to be found in Kant's expositions of the comparison argument in VL 9:5012-16, 24:38710-20. Chapter Two 56 (d) However, we cannot have any information that is reliable enough to make possible a comparison between p and that portion of reality. All our knowledge of reality is fallible. All our information about reality is potentially deceptive. We can only compare p with items (such as judgments or beliefs) whose agreement with reality is as much in need of justification as the agreement of p with reality. Expositions of the comparison argument usually make this point by claiming that a comparison between truth-bearers and reality requires something impossible, like getting outside our skins.4 (e) From this follows that, once we have endorsed a correspondence theory of truth, we cannot know which truth-bearers are true. Philosophers have drawn at least three morals from the comparison argument. Some, like Sextus Empiricus, drew a skeptical moral from it. They claim that the premises of the argument are correct and that its conclusion follows from the premises. We cannot tell true judgments, sentences, or propositions, from false ones. Others, like Putnam, drew an anti-correspondentist moral from the comparison argument. In their view, the skeptical conclusion of the argument follows from the premises, but it is unacceptable. Hence, we must reject one of the premises of the argument, namely (a). We must deny that truth is the correspondence of a truth-bearer with a portion of reality.5 Yet others, like Berkeley, drew an idealist moral from the comparison argument. They claim that the conclusion follows from the premises, but one of them, namely (d), is true only under the assumption of a realist metaphysics. According to Berkeley, it is impossible to compare a truth- 4 See, e.g., Donald Davidson, "A Coherence Theory of Truth and Knowledge," repr. in his Subjective, Intersubjective, Objective (Oxford: Oxford University Press, 2001), 133. 5 See Hilary Putnam, Reason, Truth and History (Cambridge: Cambridge University Press, 1981), 130. A partially different reconstruction of this version of the argument is in Douglas McDermid, "Putnam on Kant on Truth": 20-21. For criticism of the comparison argument in its anti-correspondentist version, see, e.g., Douglas McDermid, The Varieties of Pragmatism: Truth, Realism, and Knowledge from James to Rorty (London: Continuum, 2006), 14-45; Wolfgang Künne, Conceptions of Truth (Oxford: Clarendon, 2003), 127-29; William P. Alston, A Realist Conception of Truth (Ithaca, NY: Cornell University Press, 1996), Ch. 3. Kant, Skepticism, and the Comparison Argument 57 bearer with a portion of reality only if the latter is mind-independent.6 If that portion of reality is in some sense constructed by our minds, then we do not need to get outside our skins in order to know it. That portion of reality is, so to say, at hand. We have an immediate, non-inferential, and reliable cognitive access to it. Hence, we are able to determine which truth-bearers are true. For Berkeley, idealism enables one to escape the skeptical threat raised by the comparison argument.7 What moral did Kant draw from the comparison argument in the Critical period? Scholars give differing answers to this question. Many hold that Kant drew an anti-correspondentist moral from the comparison argument.8 Others oppose this claim, while maintaining that, for Kant, we 6 See George Berkeley, A Treatise Concerning the Principles of Human Knowledge, in The Works of George Berkeley Bishop of Cloyne, vol. 2, ed. T. E. Jessop (London, 1949), sec. 86-87. Berkeley does not use the term "comparison." However, his line of argument is at least very close to the comparison argument. Kant probably did not read the comparison argument in Berkeley's Treatise. To our best knowledge, Kant could not read English, and the Treatise was not translated into French or German in the eighteenth century. See Geoffrey Keynes, A Bibliography of George Berkeley Bishop of Cloyne: His Works and His Critics in the Eighteenth Century (Oxford: Clarendon Press, 1976). 7 Douglas McDermid draws a fourth moral from a modified version of the comparison argument: "no representationalist notion is fit to function as a regulative action-guiding ideal. In other words, understanding truth as correspondence does not furnish inquirers with rules of action" (The Varieties of Pragmatism, 37). 8 See Melchior Palágyi, Kant und Bolzano: Eine kritische Parallele (Halle: Niemeyer, 1902), 5-6; Ernst Cassirer, "Erkenntnistheorie nebst den Grenzfragen der Logik," in his Gesammelte Werke: Hamburger Ausgabe, ed. Birgit Recki, vol. 9 (Hamburg: Meier, 2001), 140-41; Gerold Prauss, Einführung in die Erkenntnistheorie (Darmstadt: Wissenschaftliche Buchgesellschaft, 1980), 152-71; María Isabel Cabrera, "Verdad y juicio reflexionante en Kant," Dianoia (Buenos Aires) 42 (1996): 81-90; Dora Vera Hofmann, Gewissheit des Fürwahrhaltens: Zur Bedeutung der Wahrheit im Fluss des Lebens nach Kant und Wittgenstein (Berlin: de Gruyter, 2000), 201-2. Robert Hanna quotes the exposition of the comparison argument in the Jäsche Logic in support of the claim that Kant does not conceive of correspondence as a comparative resemblance between judgments and objects ("The Trouble with Truth in Kant's Theory of Meaning," History of Philosophy Quarterly 10 (1993): 8, 20 n. 22; "Kant, Truth and Human Nature," British Journal for the History of Philosophy 8 (2000): 234-35). Chapter Two 58 cannot compare judgments with reality.9 James Van Cleve suggested that Kant drew an idealist moral from the comparison argument.10 In this paper, I will reconstruct Kant's version of the comparison argument and argue that Kant drew an idealist moral from this argument. Kant thinks that the comparison argument is sound only under the assumption of transcendental realism. Once one realizes that transcendental realism is false and transcendental idealism is true, one will be able to reject one of the assumptions of the argument. Transcendental idealism makes it possible to avoid the skeptical conclusion of the comparison argument. I will only focus on Kant's comments on the comparison argument in the Critical period, from 1781 onwards. This limitation is important because, arguably, Kant drew a different moral from the comparison argument in the 1760s and early 1770s.11 I will start by reconstructing Kant's version of the comparison argument in Section II. Kant rejects the skeptical conclusion of the argument because he holds that one of its premises is false. I explain why Kant rejects that premise in Section III. Section IV shows that Kant's rejection of that premise is a consequence of his transcendental idealism. 9 Among others, the following scholars hold that, for Kant, the comparison argument does not imply the falsity of the agreement formula: Ernst Henke, Zeit und Erfahrung: Eine konstruktive Interpretation des Zeitbegriffs der Kritik der reinen Vernunft (Meisenheim a. G.: Hain, 1978), 4; McDermid, "Putnam on Kant on Truth"; Jonathan A. Waskan, "Kant's Epistemic and Defining Criteria of Truth," International Studies in Philosophy 32 (2000), no. 4: 113-14; James Van Cleve, Problems from Kant (New York: Oxford University Press, 1999), 215-16; Roderich Barth, Absolute Wahrheit und endliches Wahrheitsbewusstsein: Das Verhältnis von logischem und theologischem Wahrheitsbegriff – Thomas von Aquin, Kant, Fichte und Frege (Tübingen: Mohr Siebeck, 2004), 115. Giorgio Volpe regards the comparison argument as an argument against correspondence theories of truth. He claims that Kant probably rejected that argument. See Volpe, Teorie della verità (Milan: Guerini, 2006), 122-24. Sergio L. de C. Fernandes quotes the passage of the Jäsche Logic on the comparison argument in support of the view that, "according to Kant, there is no criterion of empirical truth." See Fernandes, Foundations of Objective Knowledge: The Relations of Popper's Theory of Knowledge to That of Kant (Dordrecht: Reidel, 1985), 76. 10 See Van Cleve, Problems from Kant, 216. 11 See Thomas Nenon, Objektivität und endliche Erkenntnis: Kants transzendentalphilosophische Korrespondenztheorie der Wahrheit (Freiburg i. B.: Alber, 1986), 167-71, and Nenon, "Limitations of a Coherence Theory of Truth in Kant's Critical Philosophy," International Studies in Philosophy 26 (1994), no. 2: 39-41. Kant, Skepticism, and the Comparison Argument 59 By contrast, transcendental realism implies the endorsement of all the premises and the conclusion of the argument. Section V reformulates the argument in light of the previous discussion and it contains a final summary. The study of Kant's stance towards the comparison argument is interesting for three reasons. First, it shows how transcendental idealism provides Kant with a way to vindicate empirical knowledge and reject a classical argument for skepticism. Second, this study sheds some light on Kant's views on the justification of empirical beliefs. Third, this study suggests that the comparison argument rests on heavy presuppositions– thus, it is not inescapable as it might seem at first sight. IIReconstruction of The Comparison Argument The Jäsche Logic presents the comparison argument as follows: [T1] Truth, it is said, consists in the agreement of cognition with its object. In consequence of this mere nominal definition, my cognition, to count as true, is supposed to agree with its object. Now I can compare the object with my cognition, however, only by cognizing it. Hence my cognition is supposed to confirm itself, which is far short of being sufficient for truth. For since the object is outside me, the cognition in me, all I can ever pass judgment on is whether my cognition of the object agrees with my cognition of the object. (VL 9:50, trans. modified) Then, the Jäsche Logic makes some comments: [T2] The ancients called such a circle in explanation a diallelus. And actually the logicians were always reproached with this mistake by the skeptics, who observed that with this definition of truth it is just as when someone makes a statement before a court and in doing so appeals to a witness with whom no one is acquainted, but who wants to establish his credibility by maintaining that the one who called him as witness is an honest man. The accusation was grounded, too. Only the solution of the indicated problem is impossible without qualification and for every man. (Ibid., trans. modified) The last sentence of the comparison argument is: "all I can ever pass judgment on is whether my cognition of the object agrees with my cognition of the object." This sentence and the following comments suggest that the conclusion of the argument is: it is possible to establish whether a cognition agrees with itself, but impossible to establish whether a cognition agrees with its object. The beginning of the passage Chapter Two 60 emphasizes that truth is the agreement of a cognition with its object. Therefore, the conclusion of the argument means that it is impossible to establish which cognitions are true. I shall call the formula "truth is the agreement of a cognition with its object" the agreement formula. The first two sentences of T1 emphasize that truth is the agreement of a cognition with its object. According to some scholars, the Jäsche Logic insists on this characterization of truth because it is at stake in the comparison argument. In their view, the last step of the argument is implicit: since it is impossible to establish whether a cognition agrees with its object, the definition of truth as the agreement of a cognition with its object must be rejected.12 This interpretation is not persuasive for two reasons. First, the section on truth of the Jäsche Logic mentions an unsolvable problem. This is the problem of providing a "criterion of truth that is certain, universal, and useful in application" (VL 9:50). Such a criterion must determine "whether a cognition agrees with just that object to which it is related and not just with any object in general" (VL 9:50-51). These statements imply that true cognitions agree with the objects to which they are related. The text goes on to explain that formal logic provides criteria of truth. They are "not sufficient for objective truth, but they are nonetheless to be regarded as its conditio sine qua non. For the question of whether cognition agrees with its object must be preceded by the question of whether it agrees with itself (as to form)" (VL 9:51). These sentences imply that objective truth is the agreement of a cognition with its object. Similar statements are incompatible with the claim that the agreement formula must be rejected. Rather, they suggest that the agreement formula is correct, but does not yield a universal criterion of truth.13 12 This is the interpretation of the scholars mentioned in n. 8. 13 This is why T1 states that the agreement formula is "a mere nominal definition" of truth. According to Kant, the nominal definition of a notion is a correct definition of that notion. However, a nominal definition does not enable one to establish, for any given item, whether it exemplifies the defined notion (see my "Kant on the Nominal Definition of Truth," forthcoming in Kant-Studien (2010), 101). The criterion of truth discussed in Section III is not universal, because it can only be applied to synthetic a posteriori judgments. A statement of the Wiener Logik is sometimes cited to argue that the comparison argument led Kant to reject the agreement formula (VL 24:82237-38). However, other statements in the same section of the Wiener Logik endorse the agreement formula as a characterization of truth (VL 24:82238-8231, 82319-25, 8249-10). Kant, Skepticism, and the Comparison Argument 61 Second, at least eleven sentences in Kant's Critical corpus state that truth is the agreement of a cognition with its object.14 By contrast, nearly all passages that reject or seem to reject a correspondence characterization of truth are from the 1760s and the 1770s.15 Incidentally, the Jäsche Logic follows Kant's habit of calling truthbearers "cognitions." Another standard term for Kantian truth-bearers is "judgments."16 I will stick to Kant's linguistic usage, employing the words "cognition" and "judgment" interchangeably, to designate truth-bearers. I recommend the following reconstruction of the comparison argument, as it is outlined in the Jäsche Logic. A more detailed reconstruction of the argument will be provided in Section V. (1) Truth is the agreement of a cognition with its object. [Premise] (2) In order to establish whether a cognition agrees with its object, it is necessary to compare that cognition with its object. [Premise] (3) It is impossible to compare cognitions with their objects. [Premise] (4) It is impossible to establish which cognitions agree with their objects. [From (2), (3)] (5) It is impossible to establish which cognitions are true. [From (1), (4)] I will now explain why the comparison argument should be reconstructed as suggested above. I will dwell on how Kant might justify the endorsement of premise (3). 14 See KrV A58/B83, A191/B236, A237/B296; VLP 24:226, 324368-69, 62717-28. For slightly different formulas, see KrV A157/B196-97, A820/B848; RL 2254 (1780-89? 1776-79??), 16:287; VL 24:70929-30, 71818-20. See also VL 24:8249-10 on falsehood. 15 RL 2124 (1760-72?), 16:244; RL 2142 (1770-78?), 16:25011; RL 2143 (1771-78?), 16:251; RL 2127 (1764-69?), 16:245; VL 24:8418-21, 38722-25, 3883-4, 40220-21. By contrast, a Reflexion and an anthropology transcript from the 1770s define truth by means of the agreement formula: RL 2155 (1776-79?), 16:2546-7; VA 25:422-4. A transcript of lectures given around 1780 illustrates the comparison argument (VPE, 25:2022-25), and it contains a coherentist characterization of truth (25:222-4). However, it also contains a correspondentist characterization of truth at 25:2010-11. The same applies to the Logik Hechsel: compare VLP, 326409-10 with VLP, 324368-74, 325387-92. The only Critical text that highlights the difficulty of the comparison argument and draws a coherentist moral from it is RM 5642 (1780-83), 18:280-1. 16 Kant calls judgments "cognitions," e.g., in KrV A71/B96. He also calls concepts and intuitions "cognitions," e.g., in KrV A320/B376, and in RL 1705 (about 1776-89), 16:88. Chapter Two 62 (1) Truth is the agreement of a cognition with its object. This is stated in the first sentence of the passage of the Jäsche Logic and in many other passages in Kant's Critical corpus.17 (2) In order to establish whether a cognition agrees with its object, it is necessary to compare that cognition with its object. This claim is not explicit in the text. It is necessary to introduce it, in order to explain why the Jäsche Logic infers that it is impossible to establish which cognitions agree with their objects from the claim that it is impossible to compare cognitions with their objects. (3) It is impossible to compare cognitions with their objects. This is implied by the last statement of T1: "all I can ever pass judgment on is whether my cognition of the object agrees with my cognition of the object." I cannot judge whether my cognition of an object agrees with that object. The quoted sentence of T1 is introduced by the construct "Denn da..., so..." ("For since...then..."). The clause comprised between "Denn da" and "so" is supposed to provide a reason why I cannot judge on whether my cognition agrees with its object. That clause is: "the object is outside me, the cognition in me." This is not very enlightening. The Jäsche Logic does not explain why the fact that an object is outside me, and a cognition of that object inside me, prevents me from knowing whether they agree with one another.18 The text of the Jäsche Logic also states: "I can compare the object with my cognition...only by cognizing it." However, it is unclear why this should raise a difficulty. If an object is totally unknown to me, then I certainly cannot compare it with my cognition. Cognizing the object seems to be necessary in order to compare it with a cognition. A clearer justification of premise (3) is provided by the example of the witness in T2. In order to compare a cognition p with the object it is about, I can check whether that cognition agrees with, or is supported by, cognitions q, r, ... z of that object. Yet q, r, ... z are like the witness mentioned in T2. The witness is called to confirm the truth of a statement made in front of a court. His statements are meant to confirm the truth of that original statement. However, we do not have any reason to believe that the statements of the witness are true. Therefore, their agreement with 17 See n. 14. 18 We will see in Section IV how the disambiguation of the expression "outside me" is related to Kant's criticism of the comparison argument. Kant, Skepticism, and the Comparison Argument 63 the original statement does not provide a reason to believe in its truth. Similarly, our cognition p might agree with cognitions q, r, ... z. However, I do not have any reason to believe that q, r, ... z are true; or, at least, the reasons that I have to believe that q, r, ... z are true are not stronger than the reasons that I have to believe that p is true. Therefore, the agreement of p with q, r, ... z does not provide any reason to believe that p is true. The example of the witness raises two questions. Why should Kant hold that, in order to compare a cognition p with its object, I must take into account other cognitions of that object? Why are the reasons to believe that those cognitions are true not stronger than the reasons to believe that p is true? In order to answer these questions, it is important to understand what kind of cognitions the comparison argument is concerned with: namely, synthetic a posteriori judgments. Kant uses the term "cognition" to indicate three types of items: judgments, concepts, and intuitions. The comparison argument focuses on those cognitions that are judgments.19 The comparison argument suggests that it is impossible to justify certain judgements by comparing them with their objects. Judgments are either analytic a priori, synthetic a priori, or synthetic a posteriori. Whether it is possible to compare cognitions with their objects is irrelevant for the justification of analytic a priori judgments, such as "all humans are animals." One can prove this judgment by analyzing the meaning of the term "human" and employing the laws of formal logic (see KrV B11, A151/B190-91). This proof procedure does not require any comparison between cognitions and objects. In fact, an analytic judgment can be true even if it is not about any (actual) object. For instance, the analytic judgment "[t]hat all bodies are extended is necessarily and eternally true, whether they exist now or not, and whether that existence is brief or lengthy, or goes on throughout all time, i.e., eternally" (D 8:235; see KrV A259/B314). Whether it is possible to compare cognitions with their objects is irrelevant also for the justification of synthetic a priori judgments. Kant proves various synthetic a priori judgments in his works. His proofs are based on assumptions regarding the cognitive capacities of humans, certain features of all the objects that humans can experience, and–in some cases–the existence of inert matter and non-existence of living matter (see 19 The comparison argument concerns the possibility to establish which cognitions are true, and judgments are the only type of cognitions that can be true or false (KrV A293-94/B350; VL 24:720). Chapter Two 64 MA 4:470, 544). In Kant's view, it is possible to deduce the remaining synthetic a priori judgments from premises including only analytic judgments and synthetic a priori judgments. Those proofs do not require any comparison between cognitions and objects. We are left with synthetic a posteriori judgments. In order to claim that we cannot compare them with their objects, Kant could argue as follows. It is possible to justify a synthetic a posteriori judgment only by taking into account the deliverances of the senses, which Kant calls empirical intuitions (KrV B12). By taking empirical intuitions into account one would be able to compare synthetic a posteriori judgments with the objects they are about. In fact, when we are asked to justify our synthetic a posteriori judgments, we often make appeal to what we have seen or heard. We normally take the deliverances of the senses to convey reliable information on the features of objects. Kant seems to agree, because he often claims that we must have empirical intuitions in order to gain genuine, synthetic knowledge of reality.20 For Kant, however, empirical intuitions provide information on particular, determinate objects, only once the mind combines them with concepts. Kant writes: [T3] With us understanding and sensibility can determine an object only in combination. If we separate them, then we have intuitions without concepts, or concepts without intuitions, but in either case representations that we cannot relate to any determinate object. (KrV A258/B314)21 It is the understanding that combines intuitions with concepts. The understanding does this by formulating synthetic judgments that are based on intuitions. Therefore, if one is to rely on empirical intuitions to justify a synthetic judgment on a determinate object, one will have to take into account the judgments that are based on those intuitions, and not just those bare intuitions, which, as such, are "blind" (KrV A51/B75). When one formulates a judgment about an object out of intuitions, Kant writes, [T4] then of course there can arise deceptive representations, to which objects do not correspond, and where the deception is sometimes to be attributed to a semblance of the imagination (in dreams), sometimes to a 20 See, e.g., KrV A19/B33, A63/B87, A719/B747. 21 See Rolf George's provocative translation of KrV A51/B75-76: "[o]nly if they (the understanding and the senses, i.e. intuitions and concepts) are united can reference [Erkenntnis] result" ("Kant's Sensationism," Synthese 47 (1981): 243). Kant, Skepticism, and the Comparison Argument 65 false step of the power of judgment (in the case of so-called sense-deceptions). (KrV A376, trans. modified) The possibility of such errors might suggest that, after all, one cannot justify a synthetic a posteriori judgment just by checking its object. This is because: –in order to justify a synthetic a posteriori judgment p, one must compare p with judgments q, r, ... z, which are based on intuitions; − but those judgments might be wrong, due to the influence of dreams, hallucinations, or sense-deceptions; − therefore, one cannot have any stronger reason to believe that q, r, ... z are true than one has to believe that p is true. To overcome this difficulty, Kant might argue that one can justify a synthetic judgment p by comparing it with other judgments q, r, ... z, even if one does not have independent reasons to believe that q, r, ... z are true. Let us assume that the set {q, r, ... z} is the set of all judgments which express one's beliefs. Let S be the set of judgments p, q, r, ... z. Kant might subscribe to a coherentist account of justification. He might claim that, if the set {p, q, r, ... z} is coherent, then we have reason to believe that p, q, r, ... z are true. Using the metaphor of the tribunal, we need not have independent reasons to believe that each of our witnesses, considered individually, is truthful. The fact that their statements agree with one another provides reason to believe that all witnesses are truthful. In order to make this proposal plausible, we need to spell out the notion of coherence involved. I will assume that Kant identifies coherence with some form of systematicity: p, q, ... z are coherent if they form a system. Kant holds that a system is a body of judgments ordered according to a leading idea, general principles, and inductive and deductive relations. 22 For our present purposes, I will assume that a set S of judgments S is a system if and only if: − S is consistent, − and every member of S is either a belief which can be inferred from some other member of S, by means of inductive or deductive inferences, or a premise without which it is impossible to infer some other member of S. 22 See KrV A645/B673, A832-34/B860-62. Chapter Two 66 Kant might hold that, if a judgment p and judgments q, r, ... z, which express one's beliefs, form a system, then we have reason to believe that p, q, ... z are true. However, Kant does not endorse this view–at least not for synthetic judgments, which are at stake in the comparison argument. According to Kant, the fact that a judgment p, together with other judgments q, r, ... z, forms a system, provides reason to believe that p is true only if there are independent reasons to believe that q, r, ... z are true. If there is no independent reason to believe that q, r, ... z are true, then the fact that p, q, r, ... z form a system will not provide any reason to believe that p is true. This can be seen from two remarks. First, for Kant, the judgments of transcendental philosophy are part of a system. Kant states that "the completeness and articulation of [the system of transcendental philosophy] can at the same time yield a touchstone of the correctness and genuineness of all the pieces of cognition fitting into it" (KrV A65/B90). However, in order to persuade his readers of the truth of transcendental philosophy, Kant relies on a complex series of arguments, and not on the claim that transcendental philosophy is coherent. The quoted sentence is meant to strengthen the reader's belief in the truth of the judgments of transcendental philosophy. That belief is not based on the coherence of those judgments, but rather, on several other arguments. Second, Kant states that Wolff's philosophical system is a model of systematicity (and hence coherence), but it contains false principles, wrong definitions, and fallacious proofs. 23 One of Kant's lecture transcripts states that the philosophy of the Wolffian Baumeister "teems with errors" (VL 24:91). 24 Yet, his philosophy forms a tightly interconnected system. If this is so, then systematicity alone cannot provide reason to hold a set of judgments for true. One might reply that the systematicity of Wolff's philosophy is only apparent. It is undermined by the errors that are contained in his proofs. Kant would agree, because he holds that some of Wolff's central proofs 23 On the systematicity of Wolff's philosophy, see KrV Bxxxvi. On its false principles, see KrV A272-74/B328-30 and VM, 28:551. On its wrong definitions, see VL 24:5716-8, 7608-10, 917-18, 92130-39, 92423-26; ML 24:62436-38. On its fallacious proofs, see WP 20:309, and the Paralogisms chapter of the Critique of Pure Reason. 24 Kant is probably referring to Baumeister's Philosophia definitiva, as Norbert Hinske noted. See Hinske, Kant-Index, vol. 5 (Stuttgart: Frommann-Holzboog, 1999), lxxxvi. Kant, Skepticism, and the Comparison Argument 67 are mistaken. However, in Kant's view, this is not Wolff's greatest fault. His greatest fault is trying to prove synthetic judgments that cannot be warranted by experience. By doing this, Wolff went beyond the boundaries of synthetic knowledge, whose delineation is one of main results of the Critique of Pure Reason: the only synthetic judgments which yield knowledge of objects are those which can be supported by empirical intuitions (KrV Bxxvi n., B165-66; WP 20:266, 274) and those which describe necessary conditions of experience. 25 Not the lack of systematicity, but the disregard for the boundaries of synthetic knowledge, is the main cause of Wolff's philosophical shipwreck. Even if the judgments forming Wolff's system were linked to one another by flawless arguments, we would not have reason to hold them for true. This is because they are mostly synthetic judgments that go beyond the limits of possible experience.26 We are not justified in holding for true any synthetic judgment that goes beyond those boundaries.27 If this is correct, then mere systematicity does not provide reason to hold a set of synthetic judgments for true. Accordingly, the belonging of a synthetic judgment p to a coherent set of judgments cannot justify the belief that p is true. If one cannot compare a cognition with its object, and if comparing a cognition with other cognitions does not provide a justification for one's judgments, one will have as a last resort only the comparison of a cognition with itself. Thus, the comparison argument states: "all I can ever pass judgment on is whether my cognition of the object agrees with my cognition of the object" (VL 9:50). One can easily check whether a cognition agrees with itself, but it is obvious that it will. Only self-contradictory cognitions might not pass the test of agreement with 25 The judgments of the last type are the judgments of the Critique of Pure Reason. One who erected a philosophical system by drawing consequences from arbitrary definitions, without making sure that they apply to objects of experience, would be a "dreamer of reason," an "architect of ideal worlds," obtained "from a small quantity of building-material derived from experience and a larger quantity of surreptitious concepts" (DS-S 2:342). Wolff's system, based on such arbitrary definitions, can get a grip of reality only by means of deception: see DS-S 2:358-59. Another metaphor which aptly captures the major shortcoming of Wolff's system in Kant's eyes is the metaphor of the dove in KrV A5/B8-9. 26 Some of them are analytic judgments. 27 For the sake of simplicity, I disregard judgments stating the existence of God, human freedom, and the immortality of the soul. Those judgments go beyond the boundaries of possible experience. However, in Kant's view, we have practical reasons to hold them for true. Chapter Two 68 themselves. Yet, passing that test, Kant writes, "is far short of being sufficient for truth" (ibid.)28 The negative counterpart of the claim that it is only possible to establish whether a cognition agrees with itself is the claim that (4) it is impossible to establish which cognitions agree with their objects. From this claim and from the characterization of truth as agreement of cognitions with their objects, the Jäsche Logic infers the conclusion of the comparison argument: (5) it is impossible to establish which cognitions are true. This is a skeptical conclusion. It applies to synthetic a posteriori judgments, because the comparison of cognitions with their objects is irrelevant to the justification of analytic a priori judgments and synthetic a priori judgments. The conclusion of the argument, (5), follows from premises (1), (2), and (3). However, Kant did not endorse the conclusion of the argument, at least with regard to synthetic judgments on objects in space and time. The critical Kant was not a skeptic about objects in space and time. He held that we are justified in formulating various synthetic a posteriori judgments on those objects. Consequently, Kant is bound to deny one of the premises of the argument. In the next section, I will argue that Kant denies premise (3). This can be inferred from his statements on the criterion of empirical truth. IIIKant's Criterion of Empirical Truth Kant rejects premise (3) because he holds that it is possible to compare synthetic a posteriori judgments about objects in space and time with those objects. Comparing a synthetic a posteriori judgment p with its object is to check if p is supported by some reliable piece of information about that object. In Kant's view, we have such reliable pieces of information about 28 Kant often uses the expression "agreement of a cognition with itself" to designate the coherence of a cognition with the laws of formal logic, most notably with the law of contradiction. The statement that one can check if a cognition agrees with itself might mean that one can check if a cognition conforms to the laws of formal logic. However, for Kant, the conformity of a synthetic judgment to the laws of formal logic is an insufficient condition of truth (see KrV A7/B11, A154-55/B193-94; P 4:26727-29). It does not provide any reason to believe that a judgment is true. Kant, Skepticism, and the Comparison Argument 69 outer objects. They are those that I will call "empirically testable judgments." Comparing p with its object is to check if p is supported by empirically testable judgments. If it is, then one has a reason to hold p for true. An empirically testable judgment is a judgment with two features: it is based on the deliverances of the senses, and it conforms to the transcendental laws of knowledge. I will now explain these features. We have seen that, for Kant, the deliverances of the senses provide information on particular objects only once they are joined with concepts into judgments. In Kant's view, the activity of judging is an essential component of object perception. Every time we perceive something as an object, we perceive it as subsumed under concepts, which we ascribe to that object by means of an act of judgment.29 Perception is an involuntary process, triggered by the stimulation of our senses. Accordingly, a judgment based on the deliverances of the senses is a judgment that we spontaneously form in the course of perceptual processes. A feature of such judgments is involuntariness. The fact that, given appropriate visual inputs, I cannot help judging that "there is an object in front of me," "the chair is red," or "the cup in on the table," is a sign that those judgments are based on the deliverances of the senses. The transcendental laws of knowledge are the laws formulated in the Transcendental Aesthetic and the Transcendental Analytic of the Critique of Pure Reason. They explain how the mind generates mental representations of objects out of the deliverances of the senses. Those laws, together with other assumptions of Kant, imply that every object of which we can have experience has certain features: it is extended in an Euclidean space, it is permanent through time, it is an aggregate of parts, it has qualitative properties that can vary by degree, it undergoes changes according to the causal law, and it interacts with every other simultaneously existing object. As a consequence, a judgment on objects which we can experience will conform to the transcendental laws of knowledge only if it does not imply the existence of atemporal objects (such as God), objects which are not extended in an Euclidean space, or which are not aggregates of parts (such as Leibniz's monads), objects which do not have qualitative features that can vary by degree, objects whose changes are not subjected to the causal law, or objects that do not interact with every other simultaneously existing object. One of the transcendental laws of knowledge is the causal law. This law implies that every change of objects that we can experience has causes 29 The concepts at stake include at least the categories: see KrV B129-43. Chapter Two 70 and effects involving other objects of possible experience. Accordingly, for every judgment p which conforms to the transcendental laws of knowledge and which describes an event, it will be possible to infer p from other judgments which conform to the transcendental laws of knowledge and which describe its causes or consequences. Kant holds that we are justified in holding empirically testable judgments for true. This means that we are justified in holding a judgment for true if it satisfies the following conditions: 1. It is based on the deliverances of the senses, 2. It does not imply the existence of atemporal objects, unextended objects, simple objects, and so on, 3. And it describes an event whose occurrence can be inferred by applying the causal law to the events described by other judgments that satisfy conditions 1 and 2. We can call this criterion Kant's criterion of empirical truth. A judgment that satisfies Kant's criterion of empirical truth is an empirically testable judgment. In Kant's view, other elements concur to determine whether we are justified to hold a synthetic a posteriori judgment for true: its coherence with the laws of the Metaphysical Principles of Natural Science, its coherence with the empirical laws of nature, the possibility of including it in the system of all our beliefs,30 its coherence with the judgments of other people, etc. For the sake of simplicity, I will disregard these components of Kant's theory of justification for synthetic a posteriori judgments, and I will focus on the criterion spelled out by conditions 1-3. Kant implies that his criterion of empirical truth is valid in several passages on the distinction between waking experiences and dreaming experiences, such as the following: [T5] Cartesian idealism [...] distinguishes only outer experience from dream... Here the doubt can easily be removed, and we always remove it in ordinary life by investigating the connection of appearances in both space and time according to universal laws of experience, and if the 30 This is a coherentist component of Kant's conception of justification for synthetic a posteriori judgments. The third condition of Kant's criterion of empirical truth is another coherentist component of Kant's conception of justification. However, this conception is not a purely coherentist conception like the conception outlined in Section II. Kant, Skepticism, and the Comparison Argument 71 representation of outer things consistently agrees therewith, we cannot doubt that those things should not constitute truthful experience. (P 4:33637, italics added)31 This passage states that the "appearances" given to us are veridical if they conform to the "universal laws of experience." I take these laws to be the transcendental laws of knowledge, because, for Kant, the transcendental laws of knowledge are the only truly universal laws structuring human experience. 32 T5 states that, once one has mental representations of appearances, and hence, once one has empirical intuitions, those appearances will represent actual objects if they conform to the transcendental laws of knowledge. Accordingly, the fact that a judgment based on the deliverances of the senses conforms to the transcendental laws of knowledge provides reason to believe that such a judgment is true. Judgments that are based on the deliverances of the senses and conform to the transcendental laws of knowledge are empirically testable judgments. Therefore, for Kant, we are justified in holding empirically testable judgments for true. Empirically testable judgments provide a basis for the justification of other synthetic judgments: "[i]n experimental philosophy," Kant writes, "the ultimate means for deciding the controversy must at least lie in experience, whether it is found early or late" (KrV A425/B452). We are justified in holding a synthetic judgment a posteriori for true if it is an empirically testable judgment, or if we can infer it, inductively or deductively, from empirically testable judgments. As for the remaining synthetic judgments, Kant writes that "much must remain uncertain and many questions insoluble, because what we know about nature is in many cases far from sufficient for what we would explain" (KrV A477/B505; see also KrV A480/B508). Despite this limitation, Kant's philosophy provides us with a method to justify a wide range of synthetic judgments on the basis of experience. 31 See also KrV A492/B520-21 and the following passages: "The difference between truth and dream, however, is not decided through the quality of the representations that are referred to objects, for they are the same in both, but through their connection according to the rules that determine the combination of representations in the concept of an object, and how far they can or cannot stand together in one experience" (P 4:290-91); "space and time (in combination with the pure concepts of the understanding) prescribe a priori their law to all possible experience, which law at the same time provides the sure criterion for distinguishing truth from illusion in experience" (P 4:375). 32 Empirical laws enjoy only a "comparative universality" (KrV B3-4). Chapter Two 72 In order to compare a synthetic a posteriori judgment with its object, one must check whether that judgment is supported by the deliverances of the senses. Kant emphasizes that the deliverances of the senses must be cast into judgments, in order to justify empirical beliefs; he admits that those judgments might be wrong; and he provides a criterion to single out the judgments which we are entitled to believe, among those which are based on the deliverances of the senses. The judgments that satisfy that criterion are empirically testable judgments. Thus, in order to compare a synthetic a posteriori judgment with its object, one must ascertain whether that judgment is an empirically testable judgment or whether it can be inferred from empirically testable judgments. At this point, interpreters are faced with a choice. They could claim that checking whether a judgment is, or can be inferred from, an empirically testable judgment, does not bear any resemblance with an operation of comparison. Alternatively, interpreters could claim that checking whether a judgment is, or can be inferred from, an empirically testable judgment, is Kant's way to compare a cognition with its object. If one chooses the first option, it will follow that Kant rejects premise (2) of the comparison argument. It is possible to establish whether a synthetic a posteriori judgment or cognition agrees with its object without performing any comparison, by checking whether a judgment is, or can be inferred from, an empirically testable judgment. If one chooses the second option, it will follow that Kant endorses premise (2) of the comparison argument, but he rejects premise (3). Empirically testable judgments provide a way for comparing cognitions with objects. I will choose the second option for the following reason. At the beginning of this paper, I stated that comparing a judgment with its object means checking whether that judgment is supported by some reliable piece of information about that object–for instance, by the deliverances of the senses. Empirically testable judgments are reliable pieces of information about objects. Hence, given the above notion of comparison, checking whether a judgment is, or is supported by, empirically testable judgments, is an act of comparison. It is Kant's way to compare judgments with objects by checking whether those judgments are supported the deliverances of the senses. If this is correct, it follows that Kant rejects premise (3) of the comparison argument. This enables him to reject the skeptical conclusion of the argument, on the ground that it is based on a false assumption. But this raises the question: Who falls victim to the comparison argument? I shall now try to answer this question. Kant, Skepticism, and the Comparison Argument 73 IVThe Comparison Argument, Skepticism, and Transcendental Idealism Some of Kant's lecture transcripts state that skeptics formulated the comparison argument against dogmatists.33 In effect, according to Kant, dogmatism cannot escape the skeptical consequences of the comparison argument. This can be gathered from a passage of the first edition of the Critique of Pure Reason, where Kant discusses the position that he calls skeptical idealism. According to this doctrine, it is impossible to prove the existence of matter. Discussing this doctrine, Kant makes a general point concerning knowledge of outer objects: [T6] If we let outer objects count as things in themselves, then it is absolutely impossible to comprehend how we are to acquire cognition of their reality outside us, since we base this merely on the representation, which is in us. For one cannot have sensation outside oneself, but only in oneself, and the whole of self-consciousness therefore provides nothing other than merely our own determinations. (KrV A377-78, italics added) Kant holds that all philosophers before him were transcendental realists.34 Transcendental realists, to use the words of the last quotation, "let outer objects count as things in themselves."35 They believe that, if there are outer objects, they will be mind-independent. Transcendental realists are of two sorts: they are either dogmatists or skeptics. Dogmatists hold that it is possible to know outer objects. Skeptics deny that this is possible. For Kant, the very assumption of transcendental realism implies skepticism. By letting outer objects "count as things in themselves," transcendental realists make it impossible "to comprehend how we are to acquire cognition of their reality outside us." Dogmatism is an unstable philosophical position: those who endorse dogmatism will not be able to justify their beliefs about outer objects. Dogmatism implies skepticism. The second sentence of T6 hints at the reason for this. We have representations "in us," but we have no guarantee that they correctly 33 See VLP 228 (given Tillmann Pinder's correction for l. 272); VL 24:386-87 = VLP 74 (provided the reference to skeptics and dogmatists in 24:38614-17 concerns the argument laid out in 24:3871-22). Other texts mention skeptics, but not dogmatists: VPE 9:50, 24:20, 24:81. 34 Henry Allison argued for this broad characterization of transcendental realism in his Kant's Transcendental Idealism: An Interpretation and Defense, revised and enlarged edition (New Haven: Yale University Press, 2004), 21-34. 35 See also KrV A369, A491/B519. Chapter Two 74 represent things outside us, because "one cannot have sensation outside oneself, but only in oneself." This remark sounds similar to a remark in the comparison argument: "the object is outside me, the cognition in me." Kant's point is that our sensations and representations do not convey knowledge of things in themselves that are "outside us." Therefore, if by "external objects" we mean "things in themselves," we will not be able to know external objects. Kant's explanations of the reason why we cannot know things in themselves are of difficult interpretation and can hardly be summarized in few words. One strand of argument, which is in line with Kant's spatial metaphors in T1 and T6, goes as follows. We can know objects only on the basis of empirical intuitions.36 Empirical intuitions let us know only relational properties, and more precisely, only those properties that objects have in virtue of their relations to our cognitive apparatus. However, [T7] through mere relations no thing in itself is cognized; it is therefore right to judge that...outer sense can also contain in its representation only the relation of an object to the subject, and not that which is internal to the object in itself. (KrV B66-67)37 "That which is internal to the object in itself" is the intrinsic properties of objects. Kant holds that it is impossible to infer which intrinsic properties an object has, and hence what it is in itself, from our knowledge of its relational properties, that is, from the way it appears to us. Consequently, if outer objects are mind-independent things in themselves, it will be impossible to know outer objects.38 36 See KrV B146, B165-66. In the passage quoted above (KrV A377-78), Kant mentions sensations and not intuitions. Intuitions are non-conceptual representations that convey information about objects. One can have intuitions of objects only insofar as one's senses are stimulated or, in Kant's terms, "modified." This stimulus or modification is called sensation. What is important in the present context is that neither sensations nor intuitions let us know the intrinsic properties of objects. 37 See also KrV A285/B341; MA 4:54325-26; letter to C. F. Hellwag, 3 January 1791, 9:24513-20. For a discussion of the meaning of the quoted passage, see Van Cleve, Problems from Kant, 150-55. 38 This depends, at least in part, on the doctrine of space and time as pure forms of intuition. Many properties of things as they appear to us are related to space and time (e.g., shape, colour, and position). As things in themselves are not spatial or temporal, it is impossible to ascribe those properties to things in themselves. In addition, if things in themselves are the objects that affect our senses causing Kant, Skepticism, and the Comparison Argument 75 Kant holds that expressions such as "outer objects" and "things outside me" can be taken in two meanings. Taken in transcendental sense, "things outside me" signifies "something that, as a thing in itself, exists distinct from" me (KrV A373). It designates something that is mind-independent. Taken in empirical sense, "things outside me" signifies "things that are to be encountered in space" (ibid.) Things in themselves are outer in the transcendental sense, that is, they are mind-independent. They are not outer in the empirical sense, because they are not in space and time. The comparison argument refers to objects "outside me" in the transcendental sense, when it states: "since the object is outside me, the cognition in me, all I can ever pass judgment on is whether my cognition of the object agrees with my cognition of the object." I can never pass judgment on whether a cognition agrees with a thing in itself, or have a reason for believing that a cognition is true or false of a thing in itself.39 This is because I cannot know things in themselves, which are outside me in the transcendental sense. It is not surprising that the Jäsche Logic uses the expression "outside me" in transcendental sense in the comparison argument. Kant states that skeptics employed the comparison argument against dogmatists. Skeptics and dogmatists held that, if there are outer objects, they will exist "outside me" in transcendental sense, as mind-independent objects or things in themselves. Kant does not deny that there may be things in themselves, but he denies that objects in space and time are things in themselves–that they are "outside me" in the transcendental sense. This enables him to avoid the skeptical threat of the comparison argument. In Kant's view, –if objects in space and time are mind-independent, it will be impossible to know them; –if objects in space and time are mind-dependent, it will be possible to know them; –and transcendental idealism claims that objects and space and time are mind-dependent. empirical intuitions, then it will not be possible to infer which properties things in themselves have from the intuitions that they cause. This is because the inference from an effect to its cause is always conjectural and exposed to the possibility of error (KrV B276, A368, A372). 39 Kant makes an exception for cognitions stating that things in themselves exist, that they are not in space, and that they are not in time. According to Kant, we are justified in believing that those cognitions are true. Chapter Two 76 Short after T6, Kant writes: "[s]ceptical idealism thus requires us to take the only refuge remaining to us, namely to grasp the ideality of all appearances" (KrV A378, italics added). The skeptical idealist [T8] is a benefactor of human reason, since he requires us to open our eyes well even in the smallest steps of common experience, and not immediately to take for a well-earned possession what we perhaps obtain only surreptitiously. The utility created by these idealistic projects is now clearly before our eyes. They drive us forcefully–if we do not want to become tangled in confusions in our commonest assertions–to regard all perceptions...merely as consciousness of something that depends on our sensibility, and to regard their external objects not as things in themselves but only as representations, of which we can become immediately conscious like any other representation, but which are called external because they depend on that sense which we call outer sense... (KrV A377-78, italics added)40 The "surreptitious possession" on which skeptical idealists cast doubts is the assumption that objects in space and time are things in themselves. If one accepts that assumption, one will "become tangled in confusions," because one will be forced to admit that it is impossible to know objects in space and time. This conclusion is unacceptable for Kant. His way out of those confusions is transcendental idealism, or "to regard all external objects not as things in themselves, but only as representations." T8 states that we are immediately conscious of external objects, conceived in the transcendental idealist way.41 For Kant, we do not have to make questionable inferences from the deliverances of the senses to the features of mind-independent outer objects. The deliverances of the senses are the basis of an immediate, non-inferential knowledge of minddependent outer objects. The deliverances of the senses convey information that, once it is synthesized according to the laws of the Transcendental Aesthetic and Transcendental Analytic, constitutes genuine empirical knowledge. This is not to say that every judgment formulated on the basis of the deliverances of the senses is correct. When one formulates a judgment about objects out of empirical intuitions, "then–Kant writes in T4–of course there can arise deceptive representations, to which objects do not correspond" (KrV A376). Therefore, Kant provides a criterion to 40 This passage concerns skepticism on the existence of matter. Kant unfolds a similar line of argument regarding skepticism on causal relations in KpV 5:51-54. 41 See also KrV B276. Kant, Skepticism, and the Comparison Argument 77 individuate, among the judgments which are based on the deliverances of the senses, those which we are justified in holding for true. The validity of this criterion depends on the assumption that the objects that we perceive conform to the transcendental laws of knowledge, and this will be the case only if transcendental idealism is true. VConclusion Let us recapitulate. For Kant, the demonstrandum of the comparison argument is a skeptical claim: it is impossible to establish which cognitions are true. This claim applies to synthetic a posteriori judgments about objects in space and time. It is possible to prove this claim, by means of the comparison argument, only if objects in space and times are mind-independent, as transcendental realism claims. Given transcendental idealism, objects in space and time are mind-dependent, premise (3) of the comparison argument is false, and the argument fails to prove its skeptical conclusion. In light of the above discussion, I can now provide a more detailed reconstruction of the comparison argument than the one provided in Section II. On this fuller reconstruction, (3) is not a premise. It is inferred from two premises, (2*) and (2**). One of these premises, (2**), is the main claim of transcendental realism: objects in space and time are things in themselves. The fuller reconstruction of the argument makes it explicit that it is sound only under the assumption of transcendental realism. The objects mentioned in this reconstruction of the argument are objects in space and time. (1) Truth is the agreement of a cognition with its object. [Premise] (2) In order to establish whether a cognition agrees with its object, it is necessary to compare that cognition with its object. [Premise] (2*) If objects are things in themselves, it is impossible to compare cognitions with their objects. [Premise] (2**) Objects are things in themselves. [Premise] (3) It is impossible to compare cognitions with their objects. [From (2*), (2**)] (4) It is impossible to establish which cognitions agree with their objects. [From (2), (3)] (5) It is impossible to establish which cognitions are true. [From (1), (4)] Transcendental realism leads to skepticism because it endorses premises (1), (2), (2*), and (2**). Transcendental idealism denies the skeptical Chapter Two 78 conclusion of the comparison argument because it denies premise (2**), at least with regard to objects in space and time. All this allows Kant to draw an idealist moral from the skeptical challenge raised by the comparison argument. Transcendental realism, being unable to overcome that difficulty, leads to skepticism. Transcendental idealism, on the other hand, is able to overcome the difficulty raised by the comparison argument, and therefore guarantees the possibility to attain truth. Those who fall victim to the comparison argument are dogmatists. The comparison argument forces them to accept skepticism or, if they want to preserve the possibility of knowing synthetic a posteriori truths about external objects, to become transcendental idealists instead.42 Works Cited Allison Henry E. Kant's Transcendental Idealism: An Interpretation and Defense. Revised and enlarged edition. New Haven: Yale University Press, 2004. 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