LOGICAL REASONS
Pascal Engel
DRAFT version, revised version to appear in Philosophical Explorations, 2005
Abstract:
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.
1.Introduction
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”.
THE MORAL PROBLEM (Smith 1994)
(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”:
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
regression).
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.