In philosophy, rationalism is the epistemological
view that "regards reason as the chief source
and test of knowledge" or "any view appealing
to reason as a source of knowledge or justification".
More formally, rationalism is defined as a
methodology or a theory "in which the criterion
of the truth is not sensory but intellectual
and deductive".In an old controversy, rationalism
was opposed to empiricism, where the rationalists
believed that reality has an intrinsically
logical structure.
Because of this, the rationalists argued that
certain truths exist and that the intellect
can directly grasp these truths.
That is to say, rationalists asserted that
certain rational principles exist in logic,
mathematics, ethics, and metaphysics that
are so fundamentally true that denying them
causes one to fall into contradiction.
The rationalists had such a high confidence
in reason that empirical proof and physical
evidence were regarded as unnecessary to ascertain
certain truths – in other words, "there
are significant ways in which our concepts
and knowledge are gained independently of
sense experience".Different degrees of emphasis
on this method or theory lead to a range of
rationalist standpoints, from the moderate
position "that reason has precedence over
other ways of acquiring knowledge" to the
more extreme position that reason is "the
unique path to knowledge".
Given a pre-modern understanding of reason,
rationalism is identical to philosophy, the
Socratic life of inquiry, or the zetetic (skeptical)
clear interpretation of authority (open to
the underlying or essential cause of things
as they appear to our sense of certainty).
In recent decades, Leo Strauss sought to revive
"Classical Political Rationalism" as a discipline
that understands the task of reasoning, not
as foundational, but as maieutic.
In politics, rationalism, since the Enlightenment,
historically emphasized a "politics of reason"
centered upon rational choice, utilitarianism,
secularism, and irreligion – the latter
aspect's antitheism was later softened by
the adoption of pluralistic methods practicable
regardless of religious or irreligious ideology.In
this regard, the philosopher John Cottingham
noted how rationalism, a methodology, became
socially conflated with atheism, a worldview:
In the past, particularly in the 17th and
18th centuries, the term 'rationalist' was
often used to refer to free thinkers of an
anti-clerical and anti-religious outlook,
and for a time the word acquired a distinctly
pejorative force (thus in 1670 Sanderson spoke
disparagingly of 'a mere rationalist, that
is to say in plain English an atheist of the
late edition...').
The use of the label 'rationalist' to characterize
a world outlook which has no place for the
supernatural is becoming less popular today;
terms like 'humanist' or 'materialist' seem
largely to have taken its place.
But the old usage still survives.
== Philosophical usage ==
Rationalism is often contrasted with empiricism.
Taken very broadly these views are not mutually
exclusive, since a philosopher can be both
rationalist and empiricist.
Taken to extremes, the empiricist view holds
that all ideas come to us a posteriori, that
is to say, through experience; either through
the external senses or through such inner
sensations as pain and gratification.
The empiricist essentially believes that knowledge
is based on or derived directly from experience.
The rationalist believes we come to knowledge
a priori – through the use of logic – and
is thus independent of sensory experience.
In other words, as Galen Strawson once wrote,
"you can see that it is true just lying on
your couch.
You don't have to get up off your couch and
go outside and examine the way things are
in the physical world.
You don't have to do any science."
Between both philosophies, the issue at hand
is the fundamental source of human knowledge
and the proper techniques for verifying what
we think we know.
Whereas both philosophies are under the umbrella
of epistemology, their argument lies in the
understanding of the warrant, which is under
the wider epistemic umbrella of the theory
of justification.
=== Theory of justification ===
The theory of justification is the part of
epistemology that attempts to understand the
justification of propositions and beliefs.
Epistemologists are concerned with various
epistemic features of belief, which include
the ideas of justification, warrant, rationality,
and probability.
Of these four terms, the term that has been
most widely used and discussed by the early
21st century is "warrant".
Loosely speaking, justification is the reason
that someone (probably) holds a belief.
If "A" makes a claim, and "B" then casts doubt
on it, "A"'s next move would normally be to
provide justification.
The precise method one uses to provide justification
is where the lines are drawn between rationalism
and empiricism (among other philosophical
views).
Much of the debate in these fields are focused
on analyzing the nature of knowledge and how
it relates to connected notions such as truth,
belief, and justification.
=== Thesis of rationalism ===
At its core, rationalism consists of three
basic claims.
For one to consider themselves a rationalist,
they must adopt at least one of these three
claims: The Intuition/Deduction Thesis, The
Innate Knowledge Thesis, or The Innate Concept
Thesis.
In addition, rationalists can choose to adopt
the claims of Indispensability of Reason and
or the Superiority of Reason – although
one can be a rationalist without adopting
either thesis.
==== The Intuition/Deduction Thesis ====
Rationale: "Some propositions in a particular
subject area, S, are knowable by us by intuition
alone; still others are knowable by being
deduced from intuited propositions."Generally
speaking, intuition is a priori knowledge
or experiential belief characterized by its
immediacy; a form of rational insight.
We simply "see" something in such a way as
to give us a warranted belief.
Beyond that, the nature of intuition is hotly
debated.
In the same way, generally speaking, deduction
is the process of reasoning from one or more
general premises to reach a logically certain
conclusion.
Using valid arguments, we can deduce from
intuited premises.
For example, when we combine both concepts,
we can intuit that the number three is prime
and that it is greater than two.
We then deduce from this knowledge that there
is a prime number greater than two.
Thus, it can be said that intuition and deduction
combined to provide us with a priori knowledge
– we gained this knowledge independently
of sense experience.
Empiricists such as David Hume have been willing
to accept this thesis for describing the relationships
among our own concepts.
In this sense, empiricists argue that we are
allowed to intuit and deduce truths from knowledge
that has been obtained a posteriori.
By injecting different subjects into the Intuition/Deduction
thesis, we are able to generate different
arguments.
Most rationalists agree mathematics is knowable
by applying the intuition and deduction.
Some go further to include ethical truths
into the category of things knowable by intuition
and deduction.
Furthermore, some rationalists also claim
metaphysics is knowable in this thesis.
In addition to different subjects, rationalists
sometimes vary the strength of their claims
by adjusting their understanding of the warrant.
Some rationalists understand warranted beliefs
to be beyond even the slightest doubt; others
are more conservative and understand the warrant
to be belief beyond a reasonable doubt.
Rationalists also have different understanding
and claims involving the connection between
intuition and truth.
Some rationalists claim that intuition is
infallible and that anything we intuit to
be true is as such.
More contemporary rationalists accept that
intuition is not always a source of certain
knowledge – thus allowing for the possibility
of a deceiver who might cause the rationalist
to intuit a false proposition in the same
way a third party could cause the rationalist
to have perceptions of nonexistent objects.
Naturally, the more subjects the rationalists
claim to be knowable by the Intuition/Deduction
thesis, the more certain they are of their
warranted beliefs, and the more strictly they
adhere to the infallibility of intuition,
the more controversial their truths or claims
and the more radical their rationalism.To
argue in favor of this thesis, Gottfried Wilhelm
Leibniz, a prominent German philosopher, says,
"The senses, although they are necessary for
all our actual knowledge, are not sufficient
to give us the whole of it, since the senses
never give anything but instances, that is
to say particular or individual truths.
Now all the instances which confirm a general
truth, however numerous they may be, are not
sufficient to establish the universal necessity
of this same truth, for it does not follow
that what happened before will happen in the
same way again.
… From which it appears that necessary truths,
such as we find in pure mathematics, and particularly
in arithmetic and geometry, must have principles
whose proof does not depend on instances,
nor consequently on the testimony of the senses,
although without the senses it would never
have occurred to us to think of them…"
==== The Innate Knowledge Thesis ====
Rationale: "We have knowledge of some truths
in a particular subject area, S, as part of
our rational nature."The Innate Knowledge
thesis is similar to the Intuition/Deduction
thesis in the regard that both theses claim
knowledge is gained a priori.
The two theses go their separate ways when
describing how that knowledge is gained.
As the name, and the rationale, suggests,
the Innate Knowledge thesis claims knowledge
is simply part of our rational nature.
Experiences can trigger a process that allows
this knowledge to come into our consciousness,
but the experiences don't provide us with
the knowledge itself.
The knowledge has been with us since the beginning
and the experience simply brought into focus,
in the same way a photographer can bring the
background of a picture into focus by changing
the aperture of the lens.
The background was always there, just not
in focus.
This thesis targets a problem with the nature
of inquiry originally postulated by Plato
in Meno.
Here, Plato asks about inquiry; how do we
gain knowledge of a theorem in geometry?
We inquire into the matter.
Yet, knowledge by inquiry seems impossible.
In other words, "If we already have the knowledge,
there is no place for inquiry.
If we lack the knowledge, we don't know what
we are seeking and cannot recognize it when
we find it.
Either way we cannot gain knowledge of the
theorem by inquiry.
Yet, we do know some theorems."
The Innate Knowledge thesis offers a solution
to this paradox.
By claiming that knowledge is already with
us, either consciously or unconsciously, a
rationalist claims we don't really "learn"
things in the traditional usage of the word,
but rather that we simply bring to light what
we already know.
==== The Innate Concept Thesis ====
Rationale: "We have some of the concepts we
employ in a particular subject area, S, as
part of our rational nature."Similar to the
Innate Knowledge thesis, the Innate Concept
thesis suggests that some concepts are simply
part of our rational nature.
These concepts are a priori in nature and
sense experience is irrelevant to determining
the nature of these concepts (though, sense
experience can help bring the concepts to
our conscious mind).
Some philosophers, such as John Locke (who
is considered one of the most influential
thinkers of the Enlightenment and an empiricist)
argue that the Innate Knowledge thesis and
the Innate Concept thesis are the same.
Other philosophers, such as Peter Carruthers,
argue that the two theses are distinct from
one another.
As with the other theses covered under the
umbrella of rationalism, the more types and
greater number of concepts a philosopher claims
to be innate, the more controversial and radical
their position; "the more a concept seems
removed from experience and the mental operations
we can perform on experience the more plausibly
it may be claimed to be innate.
Since we do not experience perfect triangles
but do experience pains, our concept of the
former is a more promising candidate for being
innate than our concept of the latter.In his
book, Meditations on First Philosophy, René
Descartes postulates three classifications
for our ideas when he says, "Among my ideas,
some appear to be innate, some to be adventitious,
and others to have been invented by me.
My understanding of what a thing is, what
truth is, and what thought is, seems to derive
simply from my own nature.
But my hearing a noise, as I do now, or seeing
the sun, or feeling the fire, comes from things
which are located outside me, or so I have
hitherto judged.
Lastly, sirens, hippogriffs and the like are
my own invention."Adventitious ideas are those
concepts that we gain through sense experiences,
ideas such as the sensation of heat, because
they originate from outside sources; transmitting
their own likeness rather than something else
and something you simply cannot will away.
Ideas invented by us, such as those found
in mythology, legends, and fairy tales are
created by us from other ideas we possess.
Lastly, innate ideas, such as our ideas of
perfection, are those ideas we have as a result
of mental processes that are beyond what experience
can directly or indirectly provide.
Gottfried Wilhelm Leibniz defends the idea
of innate concepts by suggesting the mind
plays a role in determining the nature of
concepts, to explain this, he likens the mind
to a block of marble in the New Essays on
Human Understanding, "This is why I have taken
as an illustration a block of veined marble,
rather than a wholly uniform block or blank
tablets, that is to say what is called tabula
rasa in the language of the philosophers.
For if the soul were like those blank tablets,
truths would be in us in the same way as the
figure of Hercules is in a block of marble,
when the marble is completely indifferent
whether it receives this or some other figure.
But if there were veins in the stone which
marked out the figure of Hercules rather than
other figures, this stone would be more determined
thereto, and Hercules would be as it were
in some manner innate in it, although labour
would be needed to uncover the veins, and
to clear them by polishing, and by cutting
away what prevents them from appearing.
It is in this way that ideas and truths are
innate in us, like natural inclinations and
dispositions, natural habits or potentialities,
and not like activities, although these potentialities
are always accompanied by some activities
which correspond to them, though they are
often imperceptible."
==== 
The other two theses ====
The three aforementioned theses of Intuition/Deduction,
Innate Knowledge, and Innate Concept are the
cornerstones of rationalism.
To be considered a rationalist, one must adopt
at least one of those three claims.
The following two theses are traditionally
adopted by rationalists, but they aren't essential
to the rationalist's position.
The Indispensability of Reason Thesis has
the following rationale, "The knowledge we
gain in subject area, S, by intuition and
deduction, as well as the ideas and instances
of knowledge in S that are innate to us, could
not have been gained by us through sense experience."
In short, this thesis claims that experience
cannot provide what we gain from reason.
The Superiority of Reason Thesis has the following
rationale, '"The knowledge we gain in subject
area S by intuition and deduction or have
innately is superior to any knowledge gained
by sense experience".
In other words, this thesis claims reason
is superior to experience as a source for
knowledge.
In addition to the following claims, rationalists
often adopt similar stances on other aspects
of philosophy.
Most rationalists reject skepticism for the
areas of knowledge they claim are knowable
a priori.
Naturally, when you claim some truths are
innately known to us, one must reject skepticism
in relation to those truths.
Especially for rationalists who adopt the
Intuition/Deduction thesis, the idea of epistemic
foundationalism tends to crop up.
This is the view that we know some truths
without basing our belief in them on any others
and that we then use this foundational knowledge
to know more truths.
== Background ==
Rationalism - as an appeal to human reason
as a way of obtaining knowledge - has a philosophical
history dating from antiquity.
The analytical nature of much of philosophical
enquiry, the awareness of apparently a priori
domains of knowledge such as mathematics,
combined with the emphasis of obtaining knowledge
through the use of rational faculties (commonly
rejecting, for example, direct revelation)
have made rationalist themes very prevalent
in the history of philosophy.
Since the Enlightenment, rationalism is usually
associated with the introduction of mathematical
methods into philosophy as seen in the works
of Descartes, Leibniz, and Spinoza.
This is commonly called continental rationalism,
because it was predominant in the continental
schools of Europe, whereas in Britain empiricism
dominated.
Even then, the distinction between rationalists
and empiricists was drawn at a later period
and would not have been recognized by the
philosophers involved.
Also, the distinction between the two philosophies
is not as clear-cut as is sometimes suggested;
for example, Descartes and Locke have similar
views about the nature of human ideas.Proponents
of some varieties of rationalism argue that,
starting with foundational basic principles,
like the axioms of geometry, one could deductively
derive the rest of all possible knowledge.
The philosophers who held this view most clearly
were Baruch Spinoza and Gottfried Leibniz,
whose attempts to grapple with the epistemological
and metaphysical problems raised by Descartes
led to a development of the fundamental approach
of rationalism.
Both Spinoza and Leibniz asserted that, in
principle, all knowledge, including scientific
knowledge, could be gained through the use
of reason alone, though they both observed
that this was not possible in practice for
human beings except in specific areas such
as mathematics.
On the other hand, Leibniz admitted in his
book Monadology that "we are all mere Empirics
in three fourths of our actions."
== 
History ==
=== 
Rationalist philosophy from antiquity ===
Although rationalism in its modern form post-dates
antiquity, philosophers from this time laid
down the foundations of rationalism.
In particular, the understanding that we may
be aware of knowledge available only through
the use of rational thought.
==== Ajita Kesakambali (600 BCE) ====
Ajita Kesakambali was an ancient Indian philosopher
in the 6th century BCE.
He is considered to be the first known proponent
of Indian materialism, and forerunner to the
Charvaka school of Indian thought, which holds
direct perception, empiricism, and conditional
inference as proper sources of knowledge,
embraces philosophical skepticism and rejects
Vedas, Vedic ritualism, and supernaturalism.
==== Pythagoras (570–495 BCE) ====
Pythagoras was one of the first Western philosophers
to stress rationalist insight.
He is often revered as a great mathematician,
mystic and scientist, but he is best known
for the Pythagorean theorem, which bears his
name, and for discovering the mathematical
relationship between the length of strings
on lute and the pitches of the notes.
Pythagoras "believed these harmonies reflected
the ultimate nature of reality.
He summed up the implied metaphysical rationalism
in the words "All is number".
It is probable that he had caught the rationalist's
vision, later seen by Galileo (1564–1642),
of a world governed throughout by mathematically
formulable laws".
It has been said that he was the first man
to call himself a philosopher, or lover of
wisdom.
==== Plato (427–347 BCE) ====
Plato held rational insight to a very high
standard, as is seen in his works such as
Meno and The Republic.
He taught on the Theory of Forms (or the Theory
of Ideas) which asserts that the highest and
most fundamental kind of reality is not the
material world of change known to us through
sensation, but rather the abstract, non-material
(but substantial) world of forms (or ideas).
For Plato, these forms were accessible only
to reason and not to sense.
In fact, it is said that Plato admired reason,
especially in geometry, so highly that he
had the phrase "Let no one ignorant of geometry
enter" inscribed over the door to his academy.
==== Aristotle (384–322 BCE) ====
Aristotle's main contribution to rationalist
thinking was the use of syllogistic logic
and its use in argument.
Aristotle defines syllogism as "a discourse
in which certain (specific) things having
been supposed, something different from the
things supposed results of necessity because
these things are so."
Despite this very general definition, Aristotle
limits himself to categorical syllogisms which
consist of three categorical propositions
in his work Prior Analytics.
These included categorical modal syllogisms.
==== Post-Aristotle ====
Although the three great Greek philosophers
disagreed with one another on specific points,
they all agreed that rational thought could
bring to light knowledge that was self-evident
– information that humans otherwise couldn't
know without the use of reason.
After Aristotle's death, Western rationalistic
thought was generally characterized by its
application to theology, such as in the works
of Augustine, the Islamic philosopher Avicenna
and Jewish philosopher and theologian Maimonides.
One notable event in the Western timeline
was the philosophy of Thomas Aquinas who attempted
to merge Greek rationalism and Christian revelation
in the thirteenth-century.
=== 
Classical rationalism ===
Early modern rationalism has its roots in
the 17th-century Dutch Republic, with some
notable intellectual representatives like
Hugo Grotius, René Descartes, and Baruch
Spinoza.
==== René Descartes (1596–1650) ====
Descartes was the first of the modern rationalists
and has been dubbed the 'Father of Modern
Philosophy.'
Much subsequent Western philosophy is a response
to his writings, which are studied closely
to this day.
Descartes thought that only knowledge of eternal
truths – including the truths of mathematics,
and the epistemological and metaphysical foundations
of the sciences – could be attained by reason
alone; other knowledge, the knowledge of physics,
required experience of the world, aided by
the scientific method.
He also argued that although dreams appear
as real as sense experience, these dreams
cannot provide persons with knowledge.
Also, since conscious sense experience can
be the cause of illusions, then sense experience
itself can be doubtable.
As a result, Descartes deduced that a rational
pursuit of truth should doubt every belief
about sensory reality.
He elaborated these beliefs in such works
as Discourse on Method, Meditations on First
Philosophy, and Principles of Philosophy.
Descartes developed a method to attain truths
according to which nothing that cannot be
recognised by the intellect (or reason) can
be classified as knowledge.
These truths are gained "without any sensory
experience," according to Descartes.
Truths that are attained by reason are broken
down into elements that intuition can grasp,
which, through a purely deductive process,
will result in clear truths about reality.
Descartes therefore argued, as a result of
his method, that reason alone determined knowledge,
and that this could be done independently
of the senses.
For instance, his famous dictum, cogito ergo
sum or "I think, therefore I am", is a conclusion
reached a priori i.e., prior to any kind of
experience on the matter.
The simple meaning is that doubting one's
existence, in and of itself, proves that an
"I" exists to do the thinking.
In other words, doubting one's own doubting
is absurd.
This was, for Descartes, an irrefutable principle
upon which to ground all forms of other knowledge.
Descartes posited a metaphysical dualism,
distinguishing between the substances of the
human body ("res extensa") and the mind or
soul ("res cogitans").
This crucial distinction would be left unresolved
and lead to what is known as the mind-body
problem, since the two substances in the Cartesian
system are independent of each other and irreducible.
==== Baruch Spinoza (1632–1677) ====
The philosophy of Baruch Spinoza is a systematic,
logical, rational philosophy developed in
seventeenth-century Europe.
Spinoza's philosophy is a system of ideas
constructed upon basic building blocks with
an internal consistency with which he tried
to answer life's major questions and in which
he proposed that "God exists only philosophically."
He was heavily influenced by Descartes, Euclid
and Thomas Hobbes, as well as theologians
in the Jewish philosophical tradition such
as Maimonides.
But his work was in many respects a departure
from the Judeo-Christian tradition.
Many of Spinoza's ideas continue to vex thinkers
today and many of his principles, particularly
regarding the emotions, have implications
for modern approaches to psychology.
To this day, many important thinkers have
found Spinoza's "geometrical method" difficult
to comprehend: Goethe admitted that he found
this concept confusing.
His magnum opus, Ethics, contains unresolved
obscurities and has a forbidding mathematical
structure modeled on Euclid's geometry.
Spinoza's philosophy attracted believers such
as Albert Einstein and much intellectual attention.
==== Gottfried Leibniz (1646–1716) ====
Leibniz was the last of the great Rationalists
who contributed heavily to other fields such
as metaphysics, epistemology, logic, mathematics,
physics, jurisprudence, and the philosophy
of religion; he is also considered to be one
of the last "universal geniuses".
He did not develop his system, however, independently
of these advances.
Leibniz rejected Cartesian dualism and denied
the existence of a material world.
In Leibniz's view there are infinitely many
simple substances, which he called "monads"
(possibly taking the term from the work of
Anne Conway).
Leibniz developed his theory of monads in
response to both Descartes and Spinoza, because
the rejection of their visions forced him
to arrive at his own solution.
Monads are the fundamental unit of reality,
according to Leibniz, constituting both inanimate
and animate objects.
These units of reality represent the universe,
though they are not subject to the laws of
causality or space (which he called "well-founded
phenomena").
Leibniz, therefore, introduced his principle
of pre-established harmony to account for
apparent causality in the world.
==== Immanuel Kant (1724–1804) ====
Kant is one of the central figures of modern
philosophy, and set the terms by which all
subsequent thinkers have had to grapple.
He argued that human perception structures
natural laws, and that reason is the source
of morality.
His thought continues to hold a major influence
in contemporary thought, especially in fields
such as metaphysics, epistemology, ethics,
political philosophy, and aesthetics.Kant
named his brand of epistemology "Transcendental
Idealism", and he first laid out these views
in his famous work The Critique of Pure Reason.
In it he argued that there were fundamental
problems with both rationalist and empiricist
dogma.
To the rationalists he argued, broadly, that
pure reason is flawed when it goes beyond
its limits and claims to know those things
that are necessarily beyond the realm of all
possible experience: the existence of God,
free will, and the immortality of the human
soul.
Kant referred to these objects as "The Thing
in Itself" and goes on to argue that their
status as objects beyond all possible experience
by definition means we cannot know them.
To the empiricist he argued that while it
is correct that experience is fundamentally
necessary for human knowledge, reason is necessary
for processing that experience into coherent
thought.
He therefore concludes that both reason and
experience are necessary for human knowledge.
In the same way, Kant also argued that it
was wrong to regard thought as mere analysis.
"In Kant's views, a priori concepts do exist,
but if they are to lead to the amplification
of knowledge, they must be brought into relation
with empirical data".
=== Contemporary rationalism ===
Rationalism has become a rarer label tout
court of philosophers today; rather many different
kinds of specialised rationalisms are identified.
For example, Robert Brandom has appropriated
the terms rationalist expressivism and rationalist
pragmatism as labels for aspects of his programme
in Articulating Reasons, and identified linguistic
rationalism, the claim that the content of
propositions "are essentially what can serve
as both premises and conclusions of inferences",
as a key thesis of Wilfred Sellars.
== Criticism ==
Rationalism was criticized by William James
for being out of touch with reality.
James also criticized rationalism for representing
the universe as a closed system, which contrasts
to his view that the universe is an open system.
== See also
