Is skepticism a real challenge to knowledge ?

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1. We began by presenting The Magnitude of the Skeptical Challenge , emphasizing the unnatural and natural character of doubt on the one hand, and the magnitude of the challenge as it presents itself in particular in the form of Humean skepticism on the other. This was followed by a survey of the possible degrees and varieties of doubt, before presenting the new figures of skepticism in contemporary philosophy, highlighting the problems of definition and unity of skepticism; its ancient and modern versions, and in what form these variants are taken up in the figures of contemporary skepticism. We began by recalling the four attitudes we can adopt with regard to our beliefs: 1) judging them to be true and approving them: "It's true that we know a lot of things! "I know (dogmatism of all kinds); 2) I know, but only in a probable way (Carneades' version: probabilism); 3) it's impossible for me to determine whether I know or don't know, so I suspend my assent (pyrrhonism); 4) all things considered, I know nothing (dogmatic scepticism).

2. We then presented the two classic forms of skeptical challenge to knowledge: Agrippa's challenge and the Cartesian challenge.

a) The Cartesian challenge and the argument from ignorance. A skeptical hypothesis is a possibility of error that is incompatible with the knowledge we believe we have, but which we are also unable to measure as normal or not: this is the Cartesian or Putnamian scenario (H. Putnam, 1984). Hence the formulation of the skeptical enigma or "paradox": Sc1: I can't know that the skeptical hypotheses (e.g. that I'm dreaming or that I'm a brain in a vat (CC)) are false; Sc2: If I don't know that the skeptical hypotheses are false, I don't know very much; Sc3: So I don't know very much. (But I do know a lot: the conclusion is therefore "paradoxical"). The paradox can also be stated in the form of the "argument from ignorance" (DeRose, 1995: 1. I don't know that non-H; 2. If I don't know that non-H, then I don't know that O; 3. Therefore, I don't know that O). There areother possible formulations: to know that P, I must eliminate all possibilities that non-P; I can't eliminate all possibilities that non-P; therefore, I don't know that P. Or: if I know that P, then I have no reason to doubt that P; X is a good reason to doubt that P; therefore, I don't know that P.

b) Agrippa's challenge. We recall the definition of knowledge (K) given from Plato: (K): S knows that P if and only if: a) S believes that P; b) P is true; c) S is justified in believing that P. And what have been the main responses proposed to this aporetic definition of knowledge, either in the internalist versions (foundationism - Cartesian tree - and coherentism - Neurath's raft) or in the externalist versions (Dretske, Nozick, Goldman) of justification. We also recall the counterfactual formulation given by Nozick (1981) (based on the idea of a truth-sensitivity condition that we "follow through"): KT: S knows that P if and only if: 1) P is true; 2) S believes that P; 3) if P were not true, S would not believe that P; 4) if, in counterfactual situations, P were always true, S would always believe that P.

3. The first possible responses to the skeptical challenge were then proposed.

The first response is to start from common sense and invert the skeptical argument. Recall the argument from ignorance (in modus ponens): premise 1: I don't know that non-H; premise 2: if I don't know that non-H, then I don't know that O; conclusion C: therefore I don't know that O. Moore's (or common sense) argument consists in opposing the argument from ignorance (in modus tollens): premise 1': if I don't know that non-H, then I don't know that O [2]; premise 2': I know that O [non C]; conclusion: therefore I know that non-H [non 1].

A second response would be to assert the intrinsic link between knowledge and infallibility. Principle of infallibility: for any subject X, for any proposition P, if X knows that P, then X must know that the possibilities of error associated with P are false. If X knows that P, it could not be wrong about P.

But these requirements seem difficult to achieve.

A third strategy, called "relevant alternatives", could be based on several principles and ideas. First, the principle of epistemic closure (PC): if A knows that P, and if P implies Q, then A knows that Q. This strategy rejects the radicality demanded by the "Cartesian scenario". In other words: I can know that P without ruling out alternatives irrelevant to P. This solution is proposed by Fred Dretscke, for example:

You take your son to the zoo, see several zebras there, and when questioned by your son, tell him that they are zebras. Do you know that they are zebras? Well, most of us wouldn't hesitate to say yes: we know. We know what zebras look like; and besides, this is the city zoo, and the animals are in an enclosure that bears the sign "Zebras". Yet for something to be a zebra implies that it's not a mule and, in particular, that it's not a mule cleverly disguised by zoo officials to look like a zebra. Do you know that these animals are not mules cleverly disguised by zoo officials to look like zebras? (Dretske, 1970, 1015-6, in 2000, 39).

But to do this, he rejects PC, for the following reason: if we admit the PC closure principle, then it follows from the fact that the subject knows that it is a zebra (P), and from the fact that he knows what this implies, namely that it is not a disguised mule (if P then Q), that he also knows , that it is not a disguised mule (Q). Yet, in all rigor, he is not in a position to know this. So you can know (P) but not (Q). Hence the failure of the principle of epistemic closure. But the solution has its difficulties: we rely on the (problematic) concept of "relevance"; what does it mean to "rule out" a relevant alternative? How can we be sure that we have sufficiently independent empirical evidence for it not to appear as a mere petition of principle? How can we be sure that skeptical worlds are so far removed and so different from our own? Renouncing closure (PC) means being prepared to accept "abominable conjunctions" such as: I know I have two hands, but I don't know I'm not a brain in a vat.

Hence a fourth attempt: the contextualist strategy, which it's important to distinguish from the relativist position: "knowledge" is an essentially relative term, whose conditions of application and meaning vary according to context. If "P is true for me" means "I believe that P", we simply have a case of disagreement. The contextualist says that a sentence is true in one context where it is stated by X, not true in another. But in context C, the sentence is absolutely true (in short, truth itself is not contextual, which is disputed by a relativist for whom 1) truth changes over time, depending on the subject, etc.; 2) the context is determined solely by what the subject or community deems it to be. If we find ourselves in a skeptical conversational context where criteria are high, we'll agree with the skeptic that we know very little. Conversely, if we find ourselves in a non-skeptical conversational context, where the criteria are relatively low, we actually know more than we think we do, even if only in relation to these low epistemic criteria. But the contextualist strategy also presents difficulties. How can simple changes in the conversational context affect the agent's epistemic status? To know presupposes something universally true (which owes nothing to the conversational context in which one finds oneself (invarianism). By relativizing epistemic criteria to such an extent, we run the risk of holding any property to be true. Even if the criteria are quite broad in scope, is it as easily transposable to terms like "knowing", "having adequate evidence", or "being justified"? Doesn't the contextualist confuse pragmatic variability with semantic variability? Can we conclude from the fact that "here" means different things in different contexts that "here" has no fixed meaning? Doesn't someone who says "I'm here" know where they are? A major concession is made to the skeptic: that of the "hierarchical" structure of his doubts.

This means we have to look elsewhere for other, more "effective" parries.