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(this article was intially writen in French, and published in Risques)« Dans le doute, abstiens-toi » ("When in doubt, abstain yourself") says popular wisdom. The precautionary principle (in German "Vorsorgeprinzip") arose from the idea that it is appropriate to accept that there is doubt, or (scientific) uncertainty, in the knowledge of risks. A little over 20 years ago, in France, Barnier's law introduced the precautionary principle into French law for the "risk of serious and irreversible damage to the environment", commonly known as "environmental risk". A little bit more than 10 years ago, it was enshrined in the French Constitution, approved by 531 Members, thus expressing a very broad political consensus, probably also social. Today, however, the precautionary principle is mentioned in contexts as diverse as the risk of terrorist acts, but also in civil or criminal law procedures. What are the consequences of this drift in the use of the precautionary principle?Prudence, prevention, precautionIt is often accepted that precaution distinguishes prevention by the absence of risk identification. Prevention could be associated with protection against identified risks, while the notion of precaution questions possible actions in the face of risks not yet identified. As Ewald, Gollier and de Sadeleer (2009) point out, the precautionary principle in environmental matters involves three imperatives: reducing risks and avoiding emissions even when there are no short-term effects, formulating environmental quality objectives, and defining an ecological approach to environmental management. Therefore, even in the absence of certainty (and whatever the scientific knowledge at the time), the precautionary principle aims at not delaying the adoption of effective and proportionate measures to prevent irreversible damage at an acceptable cost. Other principles can complement the latter, such as the principle of information, or participation, which postulates that every citizen must have access to information relating to his environment.As Hunyadi (2004) noted, these three notions are closely related, but different, Prudence refers to proven risks, those whose existence is demonstrated or known empirically to such an extent that the frequency of occurrence can be estimated. Probability makes the risk insurable. This category includes alcohol consumption, or playing Russian roulette. Prevention targets proven risks, those whose existence is demonstrated or known empirically without however being able to estimate the frequency of occurrence. Nuclear risk probably falls into this category. Uncertainty is not about the risk, but about its probability of occurrence. The absence of probabilities normally makes the risk uninsurable by the traditional insurance industry. Precaution refers to risks for which neither the magnitude nor the probability of occurrence can be calculated with certainty, based on current knowledge. One example that has been much debated is genetically modified organisms, but we can include all the risks associated with nanotechnologies.Precaution, prevention and forecastsIn the words of Hohmann (1994), precaution arises from "the will to free oneself from the assimilative approach in order to replace it with an anticipatory approach". Anticipation and forecasting are then at the core of precaution: the precautionary principle implies anticipating risks, with the dimension of uncertainty that will accompany it. Like insurance. Except that the latter generally assumes that the hazard is beyond the control of agents, whereas precaution is concerned with endogenous risks, which should be anticipated.And when precaution becomes a legal principle, we can fall into excesses well known by science fiction fans." I'm placing you under arrest for the future murder of Sarah Marks and Donald Doobin that was to take place today," police officer John Anderton told the potential murderer in the 1956 Philip K. Dick short story Minority Report. Can one arrest someone preventively, or worse, cautiously, in the name of the precautionary principle?Yet we are not far from this science fiction scenario when we look at how the fight against terrorism works. In November 2015, as a result of the state of emergency, "administrative" searches were conducted." The objective is not to be accused of doing nothing when we had information. It is a kind of precautionary principle applied to terrorism," said a police officer in Libération. Before the summer of 2016, Eric Ciotti, Member of Parliament for Alpes-Maritimesin France, said, with regard to people with "S-type records", that "these people today must have a precautionary principle, they must be placed in a situation of detention. They can no longer be free, because they constitute a threat" (reported by Le Monde (2016)). Is that really the precautionary principle?Justice, uncertainty, hazard and precautionThe precautionary principle requires the practice of doubt, which may give the impression of "hyperbolic doubt", which lawyers sometimes attach to the concept of the inversion of the burden of proof. The adage "guilty until proven innocent" is replacing the age-old legal maxim "innocent until proven guilty", as van den Belt (2003), or Flückiger (2003), questioning the concept of proof in the test of the precautionary principle, evoked.Strangely, the words proof and probability derive from the same Latin adjective, probus. Probus ager is the field where seeds germinate and grow. What is probus is then what meets an expectation, produces, nourishes. Applied to man, it will imply goodness, honesty (probity). It is then a positive response to expectation (on the contrary, chance would be associated with the improbable, with a negative response). Probus will give probatio, the proof, later called proba. Approbare then means "prove", or even "approve", and the probabilis derivative would mean "approvable". It is this meaning which seems to have been retained by Cicero when he used probabilia to evoke possible conjectures. What is likely then contains a large psychological part, with an ethical judgment (we will approve), but also a truth judgment (we will prove). As Gaston Bachelard said, "it is through confusion between the psychological domain and the real domain that we incorporate the notion of probability" (Bachelard (1927)). The probability, however complicated the calculation behind the value may be, measures only our expectation.The right decision in an uncertain worldWe are asking the courts to rule on problems. Sometimes to establish a truth that scientists cannot establish (as in the context of environmental risk). But in everyday life, judges make many decisions. And make mistakes. In decision theory, this can be summarized in Table 1. In criminal justice, the judge - or a jury - must decide whether a person is innocent or not. Two types of errors are possible: false negatives (those found innocent) and false positives (those sent to prison).Table 1: Decision-making mechanism and errors (in French)In children's stories, false positives, it's Pierre who howls at the wolf when there's nothing (and who ends up tiring everyone, and when the wolf actually arrives, nobody believes it). When it comes to justice, a false positive is an innocent man sent to prison. It is not uncommon for a type of error to be "economically" more interesting. A cost-benefit analysis in marketing, for example, shows that soliciting someone who will refuse a product is generally less expensive than missing a good customer. In other applications, one type of error will be "socially preferable", as in public health. After a quarantine, we may prefer to convict innocent people than to have a contaminated person who leaves the contained area (and then contaminate the rest of the population). The great difficulty in decision theory is precisely to choose your errors (or rather your error acceptance rates).The right decision and mistakesVoltaire wrote in 1747, about Zadig, chosen by the King to become Prime Minister, "it is from him that nations derive this great principle: that it is better to chance to save a guilty than to condemn an innocent". This principle has long seemed correct (this is the second example in Table 2).Table 2: Example of decisions rendered 1) Realistic case 2) All innocent 3) All guiltyAs Table 2 shows, let us start from a real (or supposedly real) situation, with a judicial system that makes some mistakes: out of the 100 people tried, 10 guilty were acquitted, while 15 innocent people were sent to prison. That is 25% errors overall, even if we can imagine that the two errors are not of the same order. By declaring everyone innocent, 70% mistakes are made, which is obviously too high. But if you find everyone guilty, you make 30% mistakes. To some extent, the risks of the two types of errors are inversely related. Reducing one of them will generally be to the detriment of the other. We must recognize that there is an inevitable compromise in the design of our criminal justice system. In economics, the balance depends on our estimate of the economic (and other) costs associated with each of the two types of error. But in judicial matters, one can imagine that the moral aspect is important.In a civilized justice system, the risks of error of the first type are minimized to the extent possible, at least that is what is meant by the term "innocent until proven guilty". There is a price to pay for this cautious and civilized approach, namely that eventually many wrongdoers must be acquitted because of a "lack of sufficient evidence".Error and liabilityThe judge has experience built on a sub-population that is probably not representative of the French population. This selection bias is caused by the fact that the police had to convince a prosecutor to continue the investigations, at least to reach the investigation stage. What could almost legitimize that a judge - or in a way any person gravitating in the world of justice - has such a negative a priori, that in doubt, for fear of committing an error, he made his instinct, built from a biased population. Worse still: if a judge gets into the habit of convicting (based on the fact that there is no smoke without fire), he or she may be convinced that he or she has only been confronted with culprits. Yet it is normal to make mistakes." Errare humanum est" said Saint Augustine. The danger is that the decision-maker often confuses'fault' and'error', and for fear of committing a fault, for which he could be held responsible, he does not dare to decide. The difficulty is admitting her mistakes, and learning from her. For it must be remembered that the error of the second kind is a double error: if there is an innocent man languishing in prison, there is also - probably - a criminal still at large.Victims at the centre of justiceWith the precautionary principle, power makes society the potential victim, and invites us to objectify ourselves as such. After the Second World War, as Rechtmann (2005) showed, psychiatrists' attention shifted from trauma to victims. And this idea was then imposed on society as a whole: everyone must, in order to exist, express his suffering and arouse compassion. While "victimology" has thus made its entry into the world of psychiatry, at the same time the place of the victim has been strengthened in law. Levy (2004) has shown that today, victims are granted excessive rights, especially when they fall into certain categories (children, victims of sexual violence, acts of terrorism, etc). In this case, the victim's word is sacredized, the accused's defense therefore becomes impossible, everyone being unconsciously convinced of his guilt. In La Société des Victimes, Guillaume Erner denounces a new moral order which is being established and confers on the victim an almost sacred status, since it becomes a "secularized version of martyrs and saints".Lévy (2004) recalled that psychiatry seems to think that psychological disorders resulting from certain offenses are perfectly compatible with normal personalities. Thus, "it is considered that the absence of any visible sign of trauma not only does not exclude the crime, but in some cases, may constitute an additional indication of its reality. This is Edgar Hoover's idea, as legend has it: after being tapped, if the wiretaps confirmed suspicions, individuals were classified as "subversive", whereas if the wiretaps were inconclusive, they were classified as "subversive malicious".We are a long way from the time when Voltaire could claim to prefer having a guilty man in nature than having an innocent man in prison, demanding the lowest possible first hope error rate. By placing the victim at the centre of justice, we are now asking for a zero second species error rate. This amounts to denying the presumption of innocence: "guilty until proven innocent", relying abusively on the sacrosanct "precautionary principle".The precautionary principle is also a riskIt is now clear that the precautionary principle has set a new standard for judging responsibility and extended its ethical space. As François Ewald noted, "the one who introduces the risk must foresee it". By not taking sufficient precaution, in particular abstention, he can be held responsible. In the name of this principle, certain festive events are canceled, as reported by La Voix du Nord and France 3 during the cancellation of (major) sales last September. The precautionary principle frightens decision-makers and imposes an inertia, an unlimited conservative. Perhaps it is time to be more cautious in applying this principle.Bachelard, G. 1927, Essai sur la connaissance approchée, Vrin.Erner, G. 2006. La Société des victimes, La Découverte.Ewald, F. Gollier, C. et de Sadeleer, N. 2009, Le principe de précaution, Que sais-je ?Flückiger, A. 2003. La preuve juridique à l’épreuve du principe de précaution. Revue Européenne des Sciences Sociales, 41, 107-127.France 3. 2016. Lille : après la braderie, le semi-marathon et le 10 km annulés http://bit.ly/2dpU8eYHunyadi, M. 2004. La logique du raisonnement de précaution. Revue Européenne des Sciences Sociales, 42, 9-33.La Voix du Nord, 2016. Le principe de précaution appliqué à la lettre à la braderie du centre http://bit.ly/2dVE6tSLe Monde, 2016. Interner tous les djihadistes présumés « fichés S », le retour d’une proposition inapplicable. 14 juin 2016, http://bit.ly/2c9zHF4Lévy, T. 2004. Éloge de la barbarie judiciaire, Odile Jacob.Libération, 2015. Les perquisitions, « un principe de précaution ». 19 novembre 2015, http://bit.ly/2cQfxhYRechtmann, R. 2005. « Du traumatisme à la victime », in D. Fassin et P. Bourdelais (dir.), Les Constructions de l’intolérable. Études d’anthropologie et d’histoire sur les frontières de l’espace moral, La Découverte.Van den Belt, H. 2003. Debating the Precautionary Principle: “Guilty until Proven Innocent” or “Innocent until Proven Guilty”? Plant Physiology, 132(3), 1122–1126.Voltaire, 1747. Zadig ou la destinée.&#160;