Pascal Engel

Université de Paris-Sorbonne



       DRAFT version, revised version to appear in Philosophical Explorations, 2005





Simon Blackburn has shown that there is an analogy between the problem of moral motivation in ethics (how can moral reasons move us?) and the problem of what we might call the problem of the power of logical reasons (how can logical reasons move us, what is the force of the “logical must?”). In this paper, I explore further the parallel between the internalism problem in ethics and the problem of the power of logical reasons, and defend a version of psychologism about reasons, although not one of the Humean form.

        I discuss two forms of cognitivism: (a) a pure cognitivism and “hard” realism modelled after Dancy’s parallel conception in ethics: when we grasp logical reasons we grasp facts, which are direcly known to us, b) a Kantian form of cognitivism, based on the idea that “compulsion by reason goes with  the capacity of reflection.  I argue that (a) is implausible, and that b) fails to meet the internalist requirement. One would then seem to be left with what Dancy calls, about pratical reasoning, psychologism about reasons. Drawing on some suggestions by Blackburn and Railton , I sketch what might be such a psychologism. But it fails to account for the objectivity of logical reasons. I  argue that the relevant psychological state here is a form of knowledge of logical reasons, although of an implicit or tacit kind.






Let us start with some platitudes. Suppose that someone believes that A or B and also believes that not A. It is likely that she also believes B, or at least that he is disposed to believe it if the question whether B arises.  Now under what conditions can this transition be a rational one?

              First our thinker’s two beliefs A or B and not A, must constitute a reason for her to believe that B. And we can say that they are for her a reason to believe the third proposition because they actually entail this third proposition. It’s fact, a logical fact, as it were, that A or B and not A, therefore B, instantiate a valid argument form. In other words, the thinker has a reason, and an objective one, for believing the conclusion.

              Now it is not enough for our thinker to have a reason to believe the conclusion. When she believes the first two propositions, we expect her to believe the third not simply because she has a reason, but also because the first two propositions cause her to believe the third. So the three following claims are intuitively very plausible, and almost trivial:


(1)        When an argument form is valid or truth preserving, it is an objective fact that it is; this fact constitutes a reason for a person to infer certain things from others

(2)        Someone who grasps that an argument form is valid or a rule of inference is truth preserving is expected to infer accordingly, and to draw the appropriate conclusion

(3)         Inferring is a least partly a mental state, or it is based upon a mental state


We can formulate the same trivialities by saying that someone who believes that an inference rule is truth-preserving or an argument form is valid has a good, objective, reason to draw the appropriate conclusion, and to infer the appropriate conclusion and in virtue of this generally makes the appropriate inferences. Indeed if she masters the rule, and recognises its validity, it would be surprising that, when confronted with an argument form, that he does not infer the conclusion. Of course, mistakes are possible, and the psychology of human reasoning as well as the experience of teaching logic is replete with exceptions and counterexamples, but it is odd to suggest that when a subject knows a logical rule, knows that it is correct,  understands the sentences presented to her, recognises that an argument instantiates an inference of this form, she is not able to draw the appropriate conclusion.


And yet, it seems to be possible: inferential akrasia is possible. Lewis Carroll’s Tortoise seems to be such an inferential akratic. As everyone knows, he is presented three propositions of the form:


(A)                           P

(B)                            If P then Q

(Z )          Q


but refuses to draw the conclusion (Z), although he is ready to add as many premises of the form


(C)                           If A and B are true, then Z must be true


The Tortoise has all good logical reasons to make the inference, yet he does not do perform it. She maybe described as a logical akratic.


I have not used the word akrasia without intent. For we can draw a parallel between the logical case and the practical case, as Simon Blackburn (1995) has shown (see also Railton 1997).

        Blackburn shows that a similar problem to Carroll’s arises when we consider a piece of practical reasoning, for instance of the form:


(P)  I prefer lettuce to souvlaki

(B ) The moment of decision is at hand

(Z ) Let me choose to eat lettuce rather than souvlaki


       However many premises of the form :


            (P*) it is right to prefer lettuce to souvlaki


are added, the Tortoise still does not act.

Blackburn argues for a “Humean conclusion”:  “That there is always something else, something that is not under the control of fact and reason, which has to be given as a brute extra, if deliberation is ever to end by determining the will.” (1995: 695).

          It might seem that this is just a case of akrasia, in the sense of acting against one’s better reasons, or failing to do what one ought to do. But here the agent does not act at all, or refrains to act. On some views, this might just be a way of acting. But it is more interesting to think of it as a non-action in the sense of not inferring the expected conclusion from a practical syllogism, where the conclusion is, on many views of the practical syllogism, an action. Some philosophers think that there can be, in addition to practical akrasia, epistemic akrasia in the sense of knowingly failing to believe what one ought to believe.[1] Other philosophers doubt that there can be such an akrasia in the epistemic domain. The problem described here has similarities both with epistemic akrasia and with practical akrasia, but I intend to describe it specifically for the kind of failure which pertains to the domain of logical reasoning or inference from premises to conclusion.


        It should be clear from the outset that this problem does not concern  the justification of logical rules or laws, in the sense of answering the question : “Why are these rules valid or truth preserving?”[2], nor with the problem of the validity of reasons. I am concerned with the problem of the force of reasons, which Blackburn highlights in asking: “How can logic move the mind?” It would be wrong, however, to think that the two kinds of problems are independent, but these issues are so complex that I shall leave them aside. Our main question, then is: how can logical reasons move us?



2. The moral reasons problem and the logical reasons problem


        The similarity between the case of practical inference from practical reasons to act and the case of logical inference from logical reasons to believe can be made more explicit in the following way. Our initial three plausible propositions (1)-(3) remind us strongly of what has been called, in recent debates about meta-ethics, the “moral problem”.




(I)  Moral judgements of the form “It is right to f” express beliefs about

     facts (cognitivism)

(I)   If someone judges that it is right to f, then ceteris paribus he is

     motivated to f (internalism)

(III)  Motivation goes with desires and means-ends beliefs (Hume)


(I) is the familiar claim of cognitivism about moral judgement; (II) is the claim made by internalists about moral judgement, and (III) is the basic claim of the Humean theory of motivation.  There is a prima facie inconsistency between (I), (II) and (III). (I) and (II) clash with (III). (II) and (III) clash with (I).

     And just as there is a prima facie inconsistency between (I) –(III), there is also a prima facie inconsistency between (1)-(3), our three plausible propositions about logical inference. For the objectivity of our judgements about logical inference, together with the fact that they move us to infer accordingly, seems to clash with the fact that inferring is a mental state. For how can a fact about logical validity by itself have any effects upon my mental states? On the other hand, if something like (2) is true, that is if the fact that a thinker has a reason to draw a conclusion from given premises leads us to expect that he will draw this conclusion, then it seems quite plausible to suggest that the very act of inferring will be a mental act, or that it will depend upon certain mental states, as (3) says. But this clashes with (1), for if logical reasons , qua causal, are mental states ( particular beliefs, particular transitions in thought which constitute the act of inferring), how can they be objective, and the expression of logical facts?

              So it seems that we can we formulate an analogous problem to (1) (3) for logical judgement, for judgements of the form “It is right (logically) to infer Q” , that for judgements about the logical validity of a given inference. We might call it the “logical reasons problem”, or for short “the logical problem”:




(1’) Logical judgements (as to whether an inference is valid)  are true and express beliefs about logical facts (logical cognitivism)

(2’)  If someone recognises than an inference is valid, then ceteris paribus she should be moved to infer accordingly (logical internalism)

(3’) What moves a subject in such a case must be a psychological state (psychologism)


    (1’) is the characteristic claim made by cognitivists about logic. It is the claim that judgements about the validity of inferences express laws, or facts about an independent logical reality. (2’) might be called, in parallel with (II), internalism about logical judgements. It is the claim that judgements which express logical laws or the validity of inference are necessarily such that they move the thinker to draw the appropriate conclusion ( ceteris paribus, since he can make mistakes). (3’) is a claim which we might call psychologism about logic.


     Now, just as there is a conflict between cognitivism, internalism and Humeanism in the moral case, there is a conflict between cognitivism, internalism and psychologism in the logical case. If logical judgements express beliefs about facts about an independent logical reality, how can the belief about the facts in question move us to make the appropriate inferential move ? So there is a potential conflict between (1’) and (2’). But suppose we accept (1’) and (2’) together. How can we then accept (3’), for if what moves us to infer a conclusion is a psychological state, how can logical judgements be objective ? Psychologism about inference threatens the objectivity of logic.

     We might call (1’)-(3’) the “logical problem”. And we can formulate it as a problem about logical reasons, just as the moral problem is a problem about moral reasons: how can moral reasons motivate us ? how can logical reasons make us infer, or, in Blackburn’s phrase, move our mind? Achilles position in Carroll’s story seems clearly an instance of the cognitivist position: Achilles does dot understand why, once one recognises the validity of an inference, and that it expresses a logical fact, how one can fail to think accordingly.[3]  The Tortoise can be taken as, alternatively, an externalist about logical judgement, or a Humean.  She can be taken as an externalist because she is subject to logical akrasia: she recognizes the truth of a logical judgement, but fails to reason according to it. And she might be taken as a Humean, because, as Blackburn suggests, she lacks the appropriate mental state to perform the inference.


       But we should not push the parallel too far, for there are prima facie big differences. The moral problem concerns actions and practical reasoning, whereas the logical problem concerns beliefs and theoretical reasoning. If we take seriously the similarity between the two problems, we should take inferring as a kind of act . Certainly Carroll’s Tortoise speaks as if adding a premise to a set of propositions and accepting it[4] were sorts of actions, and acceptance of a proposition is indeed a sort of act. Certainly it is often said the conclusion of a piece of practical reasoning is an action[5]. And it may be one of the reasons why Carroll’s paradox arises. I shall come back to this. But is it sure that it is what happens in logical inference?  Sequences of the form (A)-(Z), unlike those of the form (P)-(Z), are usually taken to express the moving from one belief to another, not the moving from one act to another, or from a belief to an action. Indeed this is the difference between being motivated, in the case of moral judgement leading to action, and being moved to infer, in the case of logical judgement. In this sense, there is no such thing as a theory of motivation in the case of logical beliefs, for we are not motivated to act by them. And there does not seem to be an Humean theory of logical motivation either, for it would have to say that one of the determinants of the act of inferring is a desire, which is, on the face of it, utterly implausible. The Humean view and the internalism problem make sense in the moral case because there is, prima facie at least, a contrast between beliefs, which have a mind-to-world direction of fit, and desires, which have a world-to-mind direction of fit[6]. But in the case of logical inference, there is no question of moving from beliefs and desires to actions, but only from beliefs to beliefs. So we should be cautious not to identify the two problems. I think, nevertheless, that there is a case for the parallelism. In both the practical and the theoretical domain, there is a problem of reconciling the normative character of reasons with their explanatory character. In the practical case this distinction is often formulated as the problem of the distinction, and of the articulation between “normative” reasons and “motivating reasons”. In my simple example at the beginning, it is the problem of reconciling the fact that the thinker has a reason, with the fact that this reason is in some sense the cause of his inferring the conclusion.

           There are then, at least two requirements for giving an appropriate solution to the problem of how logic can move the mind, or the problem of the force of logical reasons, as we might call it. ( it is remiscent, of course, of Wittgenstein’s phrase: “the force of the logical must”):



(i)                the logical fact of the truth preserving  character of the inference gives a reason to infer (reason condition)

(ii)              that this reason causes appropriately the inferring (causal condition)


         But Lewis Carroll’s story shows that  another constraint must be added. For there to be the appropriate connexion between reason and causation, one should not add the inference form  A or B, not B, therefore A, or  if A then B, therefore B  among the premises of the inference, for otherwise the constraint would lead to the characteristic regression illustrated by Carroll’s story:


(iii)            the inference form should not be added as a premise (avoid




           As I have suggested, we can define, for the logical problem, positions which are counterparts of the positions we encounter with the moral problem. I shall first define two cognitivist solutions to the logical problem – How can logic move the mind ? – one inspired by what Jonathan Dancy (2000) has called, in the theory of moral reasons, the pure cognitivist view, and the other, inspired by forms of neo-Kantianism. I shall try to argue that they do not solve the problem. I shall them examine a counterpart of the Humean view, or an expressivism about logic, drawing from some remarks by Blackburn. But I shall argue that this expressivistic view works at the expense of the objectivity of logical reasons. So I will be lead to try to propose a third view, which will be based upon the notions of tacit knowledge of logical rules.



 3. Pure cognitivism about logical reasons


                  Suppose one accept (1’) and (2’). Then one is an internalist cognitivist about logical reasons. The internalist cognitivist’s position seems to be the one that is held by Achilles in Carroll’s story. Achilles seems to hold the following view:


(1)  It is a fact that the inference form Modus Ponens (MP) is truth- preserving

(2)  This fact in itself should prompt the Tortoise to infer accordingly.


         This seems also to be the position which is often attributed to Frege: once one  recognises the laws of “being-true”, which describe a special kind of fact, then one understands how they prescribe how to think, and so one is led to think accordingly. As Frege says in the preface to The Basic Laws of Arithmetic, to do otherwise would be to instantiate an hitherto unkown kind of folly”. [7]

          There are , however, two ways of understanding (1) and (2). If we understand (1) and (2) as giving a reason for the thinker to infer, we can construe the reason in two ways, just as we can construe reasons to act in two ways.

         Let us accept, as the cognitivist does, that logical reasons are facts.

Then a sentence ascribing to someone such a reason will have the following form:


        (i)  A’s reason for drawing the conclusion was (the fact) that p


 where “p” states the truth preserving argument – for instance MP.

  But it seems that the very fact that MP is a valid argument form cannot , by itself, be the reason for which the agent drew the conclusion. For it may be  fact ( logical fact, on this view) , that MP is a valid argument form, and nevertheless the agent does not recognize it as a fact, that is does not believe that the fact obtains. So (i) seems to be correct only if


                     (ii) A believed that p


 Compare, for instance, our answers to the question: “Why did he infer A

 from “A or B, and not B”?


(a)   because A follows from “A or B, and not B”

(b)  because he believed that A follows from “A or B, and not B”


  Hence we are to formulate (i) in this way:


  (iii) A’s reason for drawing the conclusion was that he believed that p


  In other words, it is not enough that p can constitute a reason for A to

  draw a conclusion from the premises. It has also to be the case that A

  is in some sense in psychological contact with this reason.


  If we talk in terms of the vocabulary of normative reasons vs motivating reasons which is used in the context of the theory of moral reasons, we have to say that our motivating reasons must be psychological states.  This is the assumption which I have identified as psychologism about reasons, and it is indeed the name which Dancy (2000) gives to this view.


On the psychological account we have a three-tier model :


normative reasons  ( logical laws)    



          motivating  reasons (recognition of logical laws)



                                  inferrings according to logical laws


Most cognitivist accounts of the capacity for deductive inference will use such  model.

        But they will have to face two main difficulties.

The first one is the implausibility of their epistemology. In general they do take our relationship with logical facts to be mediated by beliefs, but by  special faculty of intuition. But no satisfactory account has been given is this form of intuition. The second difficulty is the possibility of logical akrasia : one can recognise the truth of a logical law, or the validiaty of an inference form, and fail to infer accordingly. Just a the possibility of akrasia is a threat to moral cognitivism, the possibility of theoretical akrasia is a threat to logical cognitivism.



      In the moral case, Dancy (1993) defends instead the following view:


   (3*) A state can be motivating even if does not always motivate


    On this view, akrasia is possible.  According to (3*) a state can be sufficient for motivating on one occasion, and yet not motivate in another. Motivation depends upon the circumstance. This is why this view  deserves to be called particularism. But in his book Practical Reality, Dancy associates this view with an even stronger one. He claims that the reason relation does not hold between thinkers and their beliefs on the one hand and facts on the other hand, but only between facts and actions.

         Dancy criticizes the three-tier account for being unable to explain to us how the reasons why we act can be among the reasons in favour of acting. If there is a real division between normative reasons and motivating reasons, as the the three-tier account has it, then we are just unable to explain how the two fit together. The paradox is that it is impossible to do an action for the reason that makes it right

        As Dancy remarks (2000: 105) the paradox is even more marked in the theoretical case: for the reasons why we believe a conclusion are always other beliefs of ours – that is other believings (as mental states), and it is those believings which explain our adopting the belief in the conclusion. But then, as in the action case, the reasons why we believe are never the reasons in favour of which we believe it. (This is why there is a difference between (i) and (iii) above). And this slack between the two kinds of reasons is also why the Tortoise’s regress seems to be possible. The reasons she favours for inferring (Z) are not those why she infers (Z)


       Dancy then rejects the three-tier model. He considers that the only acceptable ascriptions of reasons are of the form (i), and not of the form (ii). Reasons cannot be anything psychological.

       Against this view Dancy holds that the reasons which motivate us are just the normative reasons, hence on his view the facts themselves. What makes you help someone who is in danger ? The fact that she is in danger, and not that you believe that she is in danger. If we apply this to the logical case, we shall say: what makes you infer B from A and if A then B? The fact that the former follows from the latter two.

         Facts, so to say, require our actions and, in the case of beliefs, our inferrings. It is in virtue of their being normative that they cause us to infer. This is more that pure cognitivism. This is pure realism.

        But this radical conception is utterly implausible. First it implies that pure logical facts have a sort of action at distance upon our minds. This is the very kind of platonism that makes Frege’s cognitivism so implausible. If we want to escape this we need to appeal to some faculty of intuition, which is as mysterious as the psychologistic version. Second, if we apply Dancy’s particularism in the logical case, it will mean that logical facts move us to infer, but they motivate us, so to say, case by case. Each situation would motivate us, or fail to motive us in its own way. The is utterly implausible, since it makes us loose the generality of logical facts.[8]



4. Non reflective cognitivism


       The utter implausibility of pure cognitivism invites us to reconsider the initial psychologistic version. The difficulty that we have with the three-tier model applied to logical reasons is that we are faced with a Charybdis and a Scylla.

        The Charybdis is that in order for a thinker to infer a conclusion for a reason, the thinker must not be blindly instantiating a mechanism, or be disposed to follow a rule which he does not grasp at all. This means that she must in some sense recognise the rationality of the transition in thought that she is instantiating, and therefore be able to reflect upon it. For otherwise the validity of the inference form could not be her reason for inferring what she does infer.

       Now suppose that we say that the thinker needs to reflect upon the validity of the argument form which her reasoning instantiates. This means that the thinker comes to know the conclusion of her deduction by reflection upon the validity of its form. But then we are embarked in the potential regression that Carroll’s paradox was meant to signal[9]. This the Scylla.

       Bill Brewer (1995), in a paper in which he adresses just this difficulty, remarks that the subject who has a rational capacity of making inferential deductive transitions in thought must not simply mirror blindly the norms of thought that she obeys, but must also be sensitive to them. This is implies a kind of awareness of what one is doing by inferring a proposition from others. But this awareness cannot be reflective. For if it were, the subject would have to present to herself the explicit general rule that he follows.


“ There is more to grasping the laws of logic or mathematical argument than simply being disposed to have one’s beliefs mirror the moves they prescribe. Epistemologically productive reasoning is not a merely mechanical manipulation of belief, but a compulsion in thought by reason, and as such involves conscious understanding of why one is right in one’s conclusion. (Brewer 1995: 242)


       This form of compulsion by reason makes, Brewer suggests, the proper link between reason and causation. It is a “causation in virtue of rationalisation”, whereby one simply sees why one is right. [10]

      In “Reason and First Person” (1998) Tyler Burge elaborates further an account along similar lines. He argues that the very concept of reason requires the concept of a subject and the notion of the first person: “To understand fully the fundamental notions associated with reason, including the notion of reasoning, judgement, change of mind, propositional attitude, point of view, one must have an employ a first person concept.” (p.249) He further argues that someone who is a subject, or a “critical reasoner” in this full sense not only must understand the evaluative norms that provide standards that count reasoning good or bad, but also that a subject who is able to understand these norms of reasons must “immediately be moved by reasons”. To understand reasons one must understand their force and application. So to be aware of these norms involves a tendency to be immediately motivated by them. (ibid. p. 252). In other words one cannot have reasons for thinking that P, or doing that P, without being able to be moved by them, and to take oneself as responsive to them, as able to implement them in one’s epistemic and practical decisions. And this also requires that one is able to ascribe these reasons to oneself, and have the concept of a first person. Hence the concepts of reason, of subjectivity and of agency are intrinsically interconnected.

       Brewer and Burge’s account of motivation by reason is cognitivistic: they take epistemic reasons or norms to express truths or facts, although facts of a normative, non empirical kind. It is also internalist, for they suggest that these epistemic reasons compel us to have the appropriate beliefs. But it is not epistemic norms by themselves which can motivate us.


      Both Brewer and Burge emphasise the intimate connection between having a reason to draw a conclusion and being moved to this conclusion, between what I have called the reason condition and the causal condition. But they do not make it less mysterious.

       For how can the fact that one sees that one is right, by a form of non reflective awareness, be at the same time the cause of one’s going from premises to conclusion? How is this supposed to escape the Humean objection that a mere cognitive state, where it belief or non reflective awareness, can make the mind move? To repeat the point somewhat rhetorically, even if it is true that “one cannot think of oneself as powerless”, and if “to understand reasons, one must understand their force in application in one’s reasoning” (p.251), how is it that reasons move us ? Burge’s description suggests that our very awareness of reasons as our reasons, and of the evaluative norms of beliefs and actions as being ours is in itself sufficient to lead us “immediately” to the appropriate beliefs and actions. But is it the case? Someone can certainly see that R is a good reason for doing A, and grant that it is his reason, and have the I  concept, but still fail to be moved by it. This is, after all, the Tortoise’s predicament.

The cognitivist solution thus seems to give us no solution, for it makes motivation by reason mysterious. It just reinstates our original problem.   

    As David Owens (2000) puts it:


“If you already have a non reflective awareness of the reasons which ought to motivate you, how does the judgement that you ought to me moved by them help to ensure that your are so moved? Such judgements look an idle wheel in our motivational economy, whether we are perfectly rational or not.” (Owens 2000: 17-18)



5.  Expressivism about logical reasons


       If one puts together Humean doubts bout the power of reasons to move us by themselves with a Humean doubt about the factual nature of reasons, then one is led to withdraw cognitivism about reasons, and to espouse a form of expressivism about them. Famously, in the moral case, this involves dropping (I) out of the picture, and endorsing both internalism and the Humean theory of motivation.

      What would it mean to endorse expressivism for logical reasons?

First it would mean to reinterpret what following an inference rule means, in the style of, for instance, Allan Gibbard’s (1991) conception of our acceptance of moral norms. We could say, mimicking Gibbard’s definition:



To say that Q follows from P is not to state some sort of fact about the relation between P and Q, but to express one’s acceptance of a system of norms that permits inferring P from Q


       There are no logical facts acting at distance. There are only acceptances of norms, and these are psychological facts about individuals. This is in line with the familiar point about Caroll’s Tortoise, that she mistakes a rule of inference for a proposition of logic. And a rule is not an abstract object, but the product of a practice of inferring.[11]

        Such a view of logic is of course much present in Wittgenstein’s remarks bout the “must”, but it can be extracted also from recent expressivist writings such as Blackburn’s book Ruling passions (1998). Blackburn actually suggests such a view of logic:


     “Logic is our way of codifying and of keeping track of intelligible combinations of commitments” (Blackburn 1998: 72)


        The norms of logic are not out there. They have be internalized through a practice of inferring. An inferential rule, on this view, need not be conscious, nor the object of a reflective thought. It can be a disposition, and like an habit, it may remain largely tacit. As Blackburn says, following a norm, both in the practical and in the theoretical domain, is the product of an “implicit, tacit or practical epistemology.” When someone challenges me, I can try to articulate the principles and the norms of this epistemology, in order to justify my assertion. It is probable that I not good at it, but it is the fact that my assertion is governed by norms, rather than my capacity to be conscious of them which is important to give meaning to my assertion (Blackburn 1998: 82).


        This, I want to suggest, is on the right track. But there are still two problems with the expressivist position.

        The first one is that logical reasons, on this view, fail to be objective. If logic reflects the structure of our implicit commitments, then its rules are just the reflection of the fact that these commitments are coherent. But we loose grip of the objectivity of logical reasons. It is not clear how we can escape the challenge raised by a Tortoise who would come to us with some deviant, non-truth preserving rule, of the kind instantiate by Prior famous connective tonk, and who would claim that this rule is conform to her pattern of commitments. There is at least a relativist threat in the expressivist view.[12]

         The second difficulty is that it is not clear that it solves our initial problem of accounting for the connection between a logical reason for inferring and the causal power of this reason. It says that our implicit practice with rules involves a disposition to infer accordingly. But the trouble is that a disposition is not, in itself, a cause. Merely being disposed to infer is not the same as being causally moved to infer. Someone can in general be disposed to accept certain inferences ( in our paradigmatic case, of modus ponens inferences) in certain circumstances and yet be prevented from assenting to the conclusion in other circumstances. The Carroll problem shows that even dispositions can be defeasible, for the tortoise could as well be said to have the disposition to infer the conclusion (Z), and still not act accordingly.[13]



         6. Tacit knowledge of logical reasons.


           We have reached the following position:


(1)   in order to solve the reason-causation problem in the case of deductive inference, we must not construe the kind of knowledge that a subject has or her logical reasons as a form of explicit  knowledge, for this would lead us to the familiar Carrolian regress

(2)   But we cannot simply assimilate our knowledge of logical rules to a form of practice or to a set of dispositions, for it would threaten the objective character of reasons, and it would fail to explain how they can cause us into rational transitions.


Of course one solution to this problem is simply to admit that reason and causation have nothing to do in common, and that it is simply an impossible requirement to demand that normative reasons be also motivating ones, or that objective reasons be also causes. The hard conitivist line which construes reasons as facts which act on us at a distance simply illustrates the implausibility of this articulation between the  normative order and the causal order. But it would be more a denial of the problem rather than a solution to it.

It seems to me, however, that the problem is not insuperable.

On the one hand, for a subject to be sensitive to a logical reason, he must not simply be aware of it, in the conscious mode. One can be a rational thinker without being able to conceptualise one’s transitions, and without being reflective about them. Rationality in logical inference does not require that one knows what kind of transitions one follows, and even less that one knows that one knows it. In Williamson’s terminology in another but related context, rationality is not “transparent” (Williamson 2000). On the other hand, a rational subject making logical inference must not simply perform blind inferences. He must be able to be aware of the validity of his inferences, even if not reflectively. On this I agree with Brewer. For  subject to have logical reasons, he must in some sense have access to his reasons.

            How can we conciliate these requirements and at the same time explain that the transitions in thought have a causal power on our inferential behaviour?


      A more promising solution consists in construing our logical reasons as based on a tacit knowledge of the inferential forms which goven our logical arguments. Such tacit knowledge is implicit, but not simply in the sense of being dispositional. It must be implicit in the sense of instantiating a causal structure in thought which must, in some sense, mirror the formal structure of our arguments. This requirement is the one that Evans (1985) and Davies (1987) have imposed upon the notion of tacit knowledge.  Tacit knowledge is this kind is required to be state, or a set of states, in the brain. They are fully causal. The point is that there must be a meachanism, which is generally reliable, and which grounds our inferential dispositions. At a sub-personal level (Davies 2000), the transitions must be instantiated in thought, and the subject need not be aware of them. But certainly this is not enough for having reasons to infer, for a blind causal mechanism, even tacitly know is not a reason. For this it is required that he can become aware of our inferential transitions at the personal, conscious, level.  If such logical knowledge is to be knowledge, it has to be knowledge of propositions which describe objective facts. So we need not renounce cognitivism about logical reasons, although the requirement of the objectivity of reasons does not force us into the kind of pure cognitivism that Dancy defends in the moral case. Nevertheless the  conception envisaged is psychologistic: a logical reason is based upon a psychological state. But the psychological state is not a conscious belief. It is a state of knowledge. Implicit knowledge of logical reasons has precedence over explicit beliefs about them.

        Neither am I saying that our normative reasons can be reduced to are psychological states of tacit knowledge. Like the cognitivist, I take reasons to beobjective . But the reasons, in order to be operative, must in some sense be known. But the requirements of logical rationality are such that they need not be all accessible to the subject. One can be logically rational, and a reasoner, without being a conscious reasoner.*












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[1] See A. Rorty 1983 , Scanlon 1998

[2]  The problem is raised forcefully by Dummett 1975. For recent analyses , see Peacocke 1993, Engel 1991 and Engel 2001. Boghossian 1999 and 2003, Williamson 2003

[3] See Engel 1991, pp. 254 –257 for a development of this idea.

[4]  “One who accepts A and B as true must  accept Z as true” (Carroll 1895)

[5]  Anscombe 1957 , p.60

[6]  This celebrated distinction is of course Anscombe’s (1957: 58)

[7]  cf. Frege 1964, p.12 . “In one sense a law asserts what is; in the other it prescribes what ought to be. Only in the latter sense can the laws of logic be called “laws of thought”: so far as they stipulate the way in which one ought to think. any law asserting what is can be conceived as prescribing the one ought to think in conformity with it, and it is thus in this sense a law of thought.”

[8]  Moral particularism, combined with pure cognitivism, and transposed to the logical case is thus strikingly similar to an actually opposite view about logical inference, Wittgenstein’s “radical conventionalism” (Dummett 19  ) according to which each new proof of a conclusion creates a new concept. See also Engel 1991: 261-62

[9] See also Railton 1997 (2003: 316-317)

[10] Something similar ot Brewer’s view is suggested by Boghossian (2003) when he talks about “blind reasoning”, but his problem is more the justificatory problem than the explanatory one which interests me here. Still, as suggested above, it is difficult to keep the two kinds of problems apart, although I cannot deal with this connexion here. In Engel 2001, I proposed a view of the justification of logical constants along the lines of Peacocke 1993, which is also connected to a psychologicla conception of inference through mental models.

[11] The proximity between the kind of moral expressivism defended by Gibbard and Blackbur, and Wittgenstein’s conception of logic is stressed by Blackburn 1990 and  Blackburn 1998, pp.81--82.

[12]  As sai above, I do not intend to deal here with the proble of the justification of logical rules. An expressivist or non factualist conception nevertheless faces hard problems with respect to this. Compare here P. Boghossian’s objections to a comparable non factualist view about the justification of the laws of logic, p.241

[13] The point is stressed by Williamson 2003, p.254.

* This paper was read at the 4rd conference of The European Society for Anaytic philosophy , at Lund University June 2002. For discussion of a distinct version, read at the conference on Mind and Action III, in Lisbon 2001, I’m indebted to Antonio Marques, Fred Dretske, and Donald Davidson.