The main references to this notion, outside the Meditations, are contained in Discourse on Method II (first rule), Regulae IlI and XII, Principles of Philosophy I 45-46 Replies to Objections II ('Thirdly,'

'Fourthly, and Appendix: Proposition IV). In Principles I, 45, perception is said to be clear when it is "present and apparent to an attentive mind." We may compare Regulae III, where intuition is described as an "indubitable conception formed by an unclouded and attentive mind" ("unclouded" connects with "distinct"). In Principles 45 a perception is said to be distinct "if it is so precise and different from all other objects that it contains within itself nothing but what is clear." In the case of severe pain, perception is said to be very clear but may not be distinct if it is confused with an obscure judgment about the cause of the pain (physical damage). So a perception may be clear without being distinct, but cannot be distinct without being clear.

Descartes's account is obscured by (1) predominance of visual analogy in exposition, (2) failure to distinguish between perception (con-ception) of objects or concepts and perception (knowledge, assur-ance) of propositions. Propositions might be his primary concern, and it is not too difficult to give a more or less precise interpretation to clear and distinct perception of a proposition. A proposition is clearly and distinctly perceived by me if I have no doubt at all that it is true after having adequately (and perhaps successfully) satisfied myselfjust what it entails and does not entail (it is clear to me what it con-tains, and so what it contains is clear to me [clearly true], since I cannot both have no doubt that p and have no doubt that p - > q, unless I have no doubt that q).

Descartes's failure to distinguish between objects or concepts, on the one hand, and propositions, on the other, comes out particularly clearly in Regulae XII. His account there of the knowledge of "simple natures" and "their blending or conjunction" is fairly clearly an account of the supposed objects of clear and distinct perception (or at least of a very important subclass of such objects). "Simple natures" are, rightly, unanalyzable concepts of a high, but not too high, level of generality. Figure is a simple nature (entailing no more general con-cept); but limit (i.e. terminus) is not, though more general than figure, applying not only to regions of space but also to stretches of time, for according to Descartes, the expression "limit" does not apply unambiguously to spaces and to times (presumably because of the categorical difference between spaces and times). Knowledge of simple natures is said to be incapable of error (according to Descartes because of their simplicity), but surely the cash value of this immunity is that simple natures are not propositions and so not the sort of things to be false (or true). And Descartes in this section speaks in one breath of knowledge of simple natures (concepts) and knowledge of their blending or combination (perhaps propositions) and of "ax-ioms" (certainly propositions).

At the time of Regulae, an early work, Descartes's position seems to have been: (1) Certain knowledge is confined to intuition and de-duction; intuition is infallible; and deduction, which is a concatenation of intuitions, is fallible only insofar as memory-mistake may be involved (no account is taken of fallacies). (2) Intuition, qua under-standing/apprehension of simple concepts, is infallible, since I cannot misapprehend or fail completely to apprehend what has no internal complexity. (3) Intuition of propositions is recognition of necessary connection between simple concepts; this consists in recognition of one concept as implicitly contained in another (cf. Kant on "ana-lytic").

So Descartes is in a position to hold that certain knowledge of propositions is really only a matter of articulated understanding of concepts. This is not at all absurd; it resembles the more or less contemporary view of an analytic proposition as one that cannot be de-nied by anyone who understands it (denial [conflicts with], counts against understanding). All the same, for Descartes it is incoherent; necessary connection between simple concepts cannot consist in one concept's being implicitly contained in another, for the containing concept would have to be complex. It is not clear how far this line of thinking survives in Descartes's later thought; "simple natures" is a technical term which does not appear in later work.

However, possible confusion between knowledge of propositions and understanding of concepts is detectable in the Meditations. Descartes's main use of clear and distinct perception is to provide a criterion of truth and certainty for propositions. But in the proof of the distinctness of mind and body, he relies on the principle that if A can be clearly and distinctly conceived or understood apart from B, then A and B are logically distinct and can exist separately. This can, of course, be represented as the clear and distinct perception (knowl-edge) of the modal proposition that it is possible that A should exist (be exemplified) when B does not exist, but I suggest that Descartes thought of this proposition as grounded on the distinct conception of A (a conception not involving the conception of B).

Finally it is important to remember that though for Descartes the primary cases of clear and distinct perception are necessary truths, not all cases of clear and distinct perception are necessary truths. "I exist" and "I have a pain" are not expressions of necessary truths, though Descartes may have failed to see clearly that the first is not.

II. How to Understand This Criterion

Discourse IV (cf. Meditations III) specifies the question at issue as being "what is requisite to the truth and certainty of a proposition?" and lays down the general rule that "whatever we conceive (Medita-tions III "perceive") very clearly and very distinctly is true," and adds that there is some difficulty in discerning what conceptions really are distinct.

One may wonder just why truth and certainty are spoken of so indifferently, since they are not identical notions (though there may be some inclination to suppose them to coincide in the area of necessary truth; it is attractive [though because of Gödel, wrong] to equate mathematical proof with provability). "Certain" occurs in at least two distinguishable contexts: (i) "it is certain that p" (label this "ob-jective" certainty), (ii) "x is certain that p" (label this "subjective"certainty). Perhaps, then, Descartes is subscribing to two rules (con-flated): (1) whatever is clearly and distinctly perceived is objectively certain, (2) whatever is objectively certain is true.

It is fairly clear that Descartes wants to hold not only that if something is clearly and distinctly perceived, it is certain, but also that only if something is clearly and distinctly perceived is it certain (or at least that only if we are satisfied that we clearly and distinctly perceive that p are we entitled to say that it is certain that p).

What status did Descartes attribute to his general rule? The natural supposition is that he thought of it as itself a necessary truth. If it is a necessary truth, then it might be either an implicit definition of "cer-tain" or the specification of a sure sign or mark of the presence or certainty. But there are indications of a different interpretation. Discourse Il (first rule) speaks of accepting only "what presented itself to my mind so clearly and so distinctly that I had no occasion to doubt it." And in Replies II ("Fourthly") Descartes says "to begin with, directly we think that we rightly perceive something, we spontaneously persuade ourselves that it is true!" He goes on: "Further, if this conviction is so strong that we have no reason to doubt concerning that of the truth of which we have persuaded ourselves, there is nothing more to inquire about, we have here all the certainty that can reasonably be desired." This suggests two further possibilities of interpreta-tion; (i) that the rule specifies a psychological fact about us that we cannot but assent to what we clearly and distinctly perceive (or think we clearly and distinctly perceive), (ii) that our only reasonable policy is to assent to what we (think we) clearly and distinctly perceive.

There are altogether, then, four possible ways of viewing the rule; it might specify:

1. Necessary truth defining certainty
2. Necessary truth specifying sure sign of certainty
3. Psychological fact about when we have to give our assent
4. Only reasonable procedure for attribution of certainty

We shall revert to at least some of these.

IlI. Difficulties Arising with Regard to Criterion

(1) Descartes regards the establishment of his general rule as consequential upon or derivative from his arrival at the certitude of his own existence. But in what way? The step is obviously not supposedto be a deductive one, so of what kind is it? It may be that Descartes thought of it as an example of so-called "intuitive induction," being led to recognition of the general necessity of an A being a B by detecting the coinstantiation of A and B in a particular case. But whether or not Descartes believed this, the nature of such a step is extremely obscure; it is not clear what function the individual case can have other than to draw attention to the possibility of a general connection between A and B, to put the idea of a general truth into one's head. But the Cogito does not seem especially qualified for this purpose, since the certainty of my existence seems to depend not notably on clear and distinct perception, but rather on (i) the fact that it is immune to the hypothesis of a malignant demon and (ii) the fact that "I exist" is one of a special class of propositions (statements) (cf.

"I am awake") whose truth is required in order that their expression should count as the making of an assertion; an utterance of "I exist" is either true or not a statement-making utterance at all. Descartes might just as well have had his attention drawn to the general rule by, for example, the simple arithmetical propositions which initially he seems to have regarded as open to doubt; indeed, if such examples were no good to him to begin with (as being questionable), then they will remain questionable even after the general rule is accepted; and this Descartes does not want.

One may, of course, diagnose a condition A on which a particular feature B (e.g. certainty) depends by considering what is common to clear cases of B and seeing what we seem to go by in ascribing B; but for this we need consideration of a range of examples, not just a single one (e.g. the Cogito). And the existence of such a range (cf. mathematical examples) is just what Descartes seems initially to put in ques-tion.

(2) The well-known Cartesian circle presents another difficulty.

Descartes seems to say that the acceptability of the general rule is dependent on the acceptability of the existence of a beneficent God— a malignant demon might deceive us even about what we clearly and distinctly perceive. But the existence of God needs proof, and the premises and conclusion of such a proof must be accepted on the grounds that they are clearly and distinctly perceived. But this involves a reliance on the criterion in advance of its guarantee from God.

In Replies Il Descartes answers that he never intended the beneficence of God to guarantee the general rule; what he intended it toguarantee was the reliance, in the conduct of a proof, on one's memory that certain propositions have been successfully proved, the proofs of which are not any longer before one's mind.' He is being somewhat disingenuous in this answer. Admittedly in Meditations V he does put forward just the position he outlines in Replies Il, but at the beginning of Meditations Ill he does explicitly say that the use of the general rule to reestablish simple arithmetical propositions questioned in Meditations I has to wait upon the proof of the existence of God. Descartes has in fact spoken with two voices, and will not admit it.

In any case, the favored position is not without its own difficulties:

(i) Two of Descartes's proofs of the existence of God are extremely elaborate and could not be conducted without an (unguaranteed) reliance on memory. However, the Ontological Proof is very short, and maybe Descartes could say that here reliance on memory is not in-volved.

(ii) It looks as if the beneficence of God will guarantee too much, for if it guarantees every reliance on memory, then we should not be able to make the memory-mistakes we all know that we do make.

And if it guarantees only some memory, how do we characterize and identify the kind of memory that is guaranteed?

Descartes, it seems to me,

has a perfectly good line at his disposal

here with regard to memory, analogous to the one he takes in Meditations VI about the material world. Very baldly put, his position there is that there are all sorts of ordinary nophilosophical doubts and beliefs about the material world, which we are in a perfectly good position to resolve or correct, provided that we can rely on the general assumption that our sensory ideas are generated by material objects (and perhaps, it should be added, on the assumption of the legitimacy of certain checking procedures). That our sensory ideas are so generated (and perhaps that these procedures are legitimate) is "les-son of nature"; something we are naturally disposed to believe; but if skeptical philosophical doubts are raised about them, we have no way of meeting these doubts; if our natural beliefs are incorrect, we have no way of discovering that they are. We need to know that God is no deceiver in order to be sure that we have not been constituted with a

1. Iam informed that Cartesian scholars no longer take seriously the suggestion that the function of Descartes's criterion was to justify a reliance on memory in the conduct of demonstration. This idea was, however, discernibly alive at the time when this essay was written.built-in set of erroneous natural beliefs. (For all this cf. Hume on natural dispositions.)

Similarly, Descartes could say we are in a position to correct or confirm erroneous or dubious memory claims (ideas of memory), provided we can assure that memory claims are in general generated by past events and situations, and provided that certain checking procedures (considerations of recency, distinctness, and coherence) are le-gitimate. But if the skeptic attacks these, we have no recourse, save to the beneficence of God, which would preclude our having been created with natural tendencies to assume that memory ideas in general correspond with the past, when in fact there is no such general cor-respondence. The proof of God's existence is required solely to defend us from the Skeptic and does not provide for the infallibility of memory.

(3) It has been argued by Prichard in "Knowledge and Perception" that Descartes is attempting to fulfill an impossible task, namely to provide a universally applicable mark or criterion of certainty (or, what comes to the same thing) of knowledge. He is trying to specify a mark (being a state of clear and distinct perception) such that, if and only if we can recognize our state of mind as regards some proposition p as exemplifying M can we call it a state of knowledge that

p. Any such attempt fails on account of two different vicious circles/ regresses. (i) To know that a state S is a state of knowledge that p, we need to know that it exemplifies M; but to know this, we need to know that our state S, with regard to the proposition that S exemplifies M itself exemplifies M and so on. (ii) To know that the general rule is true, we have to know that our state of mind with respect to the general rule exemplifies M, but this information is no use to us unless we can already use the rule (i.e., already know it to be true).

We have to use the rule to certify itself.

These objections may well be fatal to any attempt to provide an absolutely general sure sign of certainty (interpretation 2). But Descartes may not be making such an attempt. The objections would not, I think, apply against interpretation (1) (the definitional variant); but if we take Descartes in this way, there are other objections. For while it might be legitimate to define "x is certain that p" as "x clearly and distinctly perceives that p," it would not be so attractive to attempt to define "it is certain that p" (objective certainty) in terms of clear and distinct perception. Indeed, the problem about certainty might be posed as the question when and how a step from "I am certain" to

"it is certain" is justified.I am inclined to think that Descartes was, not very clear-headedly, espousing interpretation (4), insofar as this is distinct from interpretation (3). To amplify this, I will mark some distinctions which may be of general philosophical interest. For any proposition or range of propositions three different kinds of conditions may be specifiable, which I shall call:

1. Truth-conditions
2. Establishment-conditions
3. Reassurance-conditions

Let me consider these in relation to a class of propositions in which Descartes was specially interested, namely mathematical proposi-tions.

(1) Truth-conditions will be explicit or implicit definitions. For any given proposition or propositions a wide variety of alternative specifications may be available; which one selects will depend on one's interests, on what the concepts are to which one is concerned to link the concepts involved in the original proposition or range of propo-sitions. One might, for certain purposes, wish to specify the truth-

conditions for * = z: * = z is true iff the result of adding z to itself

y - 1 times is identical with x.

1. Establishment-conditions. These would be specifiable for a given system of mathematical propositions. A proposition p would be established if there has been found a proof of it within the system; if (that is) starting from such-and-such axioms, it has been possible to reach, in a finite number of steps constructed in accordance with such-and-such inferential rules, an expression of p.
2. Reassurance-conditions. The establishment-conditions will specify a procedure or achievement, which, if successfully realized, guarantees that p. But the question might arise whether the achievement or procedure has after all been successfully realized, whether something may not have gone wrong, and if such a question is not disposed of, we are not in a position to say "it is certain that p," even though in fact nothing may have gone wrong. So we need directions like "Go over the proof again (and if necessary again), looking out for misapplications of inferential rules, etc." Such specifications of reassurance-conditions have two notable features: (1) They are exceedingly unexciting, though supplementary directions, about what sort of mistakes to look out for, may be of general interest. And just because the specifications are liable to be general in character and

unexciting, to put this into execution may require considerable skill and intelligence; it is not a mechanical operation. (2) Reassurance-conditions are open-ended: there is no point at which carrying them out is finally completed. One can always check again, though at some point (usually quite soon) it will become unreasonable to insist on further checking. But there is no general way of specifying precisely when that point is reached.

A partial application of these ideas to propositions about physical objects may have some philosophical point. What would be an appropriate method of specifying truth-conditions in a general form for material object propositions is not clear to me, and I shall not attempt the task. But it is fairly clear how establishment-conditions should be specified, at least for the optimal or favored method of establishing a central class of material object propositions, those about "medium-size" objects. To establish p in such cases is perceptually to observe that p. Since the achievement of perceptual observations may fail to be successfully realized (something may go wrong, not usually as the fault of the observer but rather as the fault of nature), we have re-assurance-directives such as "Make further observations, bring different senses into play, compare your observational findings with those of others etc." It seems to me that the phenomenalist may have made the mistake of taking what is a perfectly sound reassurance-directive and dressing it up so as to serve as a specification of truth-conditions for material object propositions in general. The stock objection to the phenomenalist, that his analyses are not completable and have to be supposed to be of infinite length, is worth bearing in mind here, for it may be a way of making the point that the open-endedness which is characteristic of reassurance-directives becomes objectionable if the attempt is made to convert reassurance-directives into specifications of truth-conditions.

The bearing of this discussion of Descartes is that I am suggesting that his general rule should be looked upon as an attempt to provide a reassurance-directive of maximal generality, one that will apply to all propositions which can ever be said to be certain, regardless of what their truth-conditions are, what their specific establishment-conditions are, and what more specific reassurance-directives are applicable once the establishment-conditions are identified. The directive is in effect "Take all steps to satisfy yourself just what a given proposition entails and does not entail, and that having done this, you can find no ground for doubting the proposition in question."Whether the provision of a maximally generalized reassurance-di-rective is a proper philosophical undertaking and whether, if it is, Descartes has adequately discharged it, are larger questions than it is the purpose of this essay to decide. I wish to argue only (1) that it is not obvious and has not been proved that it is an improper philosophical undertaking and (2) that if it is a proper undertaking, then it is not easy to see how to improve upon Descartes's attempt to fulfill it. Our primary concern should, I think, be to ask, not whether Descartes's criterion is acceptable, but how and with what justification he has managed, by the application of what is apparently so unexceptionable a principle, to make at least plausible a skeptical position which is an affront to common sense. H. P. Grice.