“In Defense of the a Priori” by Laurence BonJour

Here, we’ll look at the two ‘dialectical’ arguments, as BonJour calls them, in defense of a priori reasons

put forth by BonJour in his paper ‘In Defense of the a Priori’ (Contemporary Debates in Epistemology).

He also has an argument from examples but we’ll not concern ourselves with that one here. At the start

of the paper, he makes it clear that he is not concerned with a priori knowledge. Rather, he is concerned

with a priori reasons. In fact, he thinks that ‘a priori’ can be relevantly applied only to justification. One

interesting question that arises here: How to draw the distinction between knowledge and justification?

Knowledge, as we know it, is justified true belief or true belief with justification\account. But, if one

takes a second look at that account of knowledge, one realizes that justification, like a knowledge claim,

is propositional in form, and hence another knowledge claim in itself. Given this, it would be interesting

to investigate how BonJour sees the two terms in question—since he insists that he is presenting a

defense for a priori justification, and not a priori knowledge. In any case, I’ll first quote the sections that

contain his arguments and then try to set out them:

“[E]xperience can provide a good reason for thinking that a belief in this category [‘indirectly

justified class of beliefs’] only if we have a logically prior good reason for believing some

conditional proposition having a conjunction of beliefs for which there are direct experiential

reasons as antecedent and the further belief we are focusing on as consequent….” (Arg 1)

“[A] reasoned or argumentative transition from a claim or group of claims to some further

conclusion relies again on there being a good reason for thinking that a conditional claim is true,

in this case one having the conjunction of the premises as its antecedent and the conclusion in

question as its consequent. That such a conditional is true (or probably true) is in general not the

sort of thing that could be directly established by experience, while to say that it is itself arrived

at via some further process of reasoning is only to raise the identical issue about the previous

step…if we never have a priori reasons for thinking that if one claim or set of claims is true, some

further claim must be true as well, then there is simply nothing that genuinely cogent reasoning

could consist in. In this way…the rejection of a priori reasons is tantamount to intellectual

suicide.” (Arg 2)

Argument 1

P1. If a belief, B, is not-justified by experience (~JEB), then there must be logically prior reason for

{(b1&b2…&bn) -> B}, where (b1&b2…&bn) is a conjunction of beliefs that are directly justified by

experience.

P2. If b1, b2,…bn are directly justified by experience and if B is irreducible to the conjunction of b1,

b2,…bn, then experience cannot directly justify {(b1&b2…&bn) -> B}.

P3. b1, b2,…bn are directly justified by experience.

P4. ~JEB.

P5. B is irreducible to the conjunction of b1, b2,…bn (since P4).

P6. Then, experience cannot directly justify {(b1&b2…&bn) -> B}.

P7. Therefore, {(b1&b2…&bn) -> B} is justified a priori.

Argument 2

P1. In a valid argument, the conclusion follows from a set of premises.

P2. P1 if and only if there is justification for the truth of a conditional claim.

P3. The truth of a conditional claim can be justified either a posteriori or a priori (A) OR the truth of

a conditional claim cannot be justified (~A).

P4. Therefore, the truth of a conditional claim must be justified a priori.

If {(p->q)&p}->q (P), then there is a good reason for thinking that a conditional claim is true (Q).

P1. Q cannot be established by experience.

P2. Q can be established by another argument (conditional in form, involving transition from

premisses to conclusion), but this doesn’t answer the issue—what establishes the truth of the

conditional claim? Only leads to further regress.

P3. Therefore, Q can only be established a priori.

If experience can provide a good reason for thinking that a belief in this category is true, then we have a

logically prior good reason for believing some conditional proposition having a conjunction of beliefs for

which there are direct experiential reasons as antecedent and the further belief we are focusing on as

consequent

Laurence is concerned with a priori justification for believing something to be true, not with a priori

knowledge as such.

His assumptions:

1. Justification is one of the requirements for knowledge—the only one to which the issue of a

priori status is relevant.

2. Justification in the relevant sense consists in having a good reason for thinking that the belief in

question is true.

The two basic elements of the concept of an a priori reason are:

1. Negative—negatively, an a priori reason for thinking that a claim is true is one whose rational

force or cogency does not derive from experience, either directly (as in perception) or indirectly

(as by inference of any sort – deductive, inductive, or explanatory – whose premises derive their

acceptability from experience).

2. Positive—positively, in the most cases a priori reasons result from similar insights into the truth,

indeed the necessary truth, of the relevant claim. Let’s call them “a priori insights”.

A priori reason negatively understood, does not mean that:

1. Someone who has undergone no experience of any sort could be in possession of it, since the

possession of an a priori reason requires understanding the claim for which it is a reason, and

experience, even experience of some fairly specific sort, might be required for that.

2. That experience of some sort could not also count for or against the claim in question.

3. That such experiences could not override, perhaps even more or less conclusively, the a priori

reason in question.

4. That an a priori reason renders the claim certain or infallible.

Difference between a priori insights and hunches or fears:

A priori insights at least reveal not just that the claim is or must be true but also why this is and indeed

must be so. Also, it is often a mistake to think of a priori insights as propositional in form. In the most

fundamental cases (modus ponens), the application of a propositional insight concerning the cogency of

such an inference would require either a further inference of the very sort in question or one equally

fundamental, thereby leading to vicious regress. Instead the relevant logical insight must be construed

as non-propositional, as a direct grasping of the way in which the conclusion is related to the premises

and validly flows from them.

The argument for a priori reasons from examples:

1. 1 + 1 = 2

2. All squares have four edges.

3. For any propositions P and Q, if it is true that P or Q and it is false that P, then it is true that Q.

4. If A > B and B > C, then A > C.

5. No surface can be uniformly read and uniformly blue at the same time.

Dialectical Arguments for a priori reasons

First argument: It is concerned with the relation between experience and certain of the beliefs which it

intuitively seems to justify. On any account of the justificatory force of experience, there will be some

beliefs whose justification derives from a direct relation to experience and others whose relation to

experience is less direct. The most straightforward version of this picture would be a broadly

foundationalist view in which the more directly justified beliefs are justified by the content of experience

alone, without the need for any reasoning or any further premises.

The class of beliefs that are broadly empirical but clearly not justified by a direct relation to experience is

extremely large and important, something that is so for any conception of the scope of direct

experiential justification that has ever been seriously advocated. This indirectly justified class of beliefs

will include at least:

1. beliefs about the unobserved past

2. beliefs about unobserved situations in the present

3. beliefs about the future

4. beliefs in laws of nature and similar sorts of generalizations

5. beliefs about unobservable entities and processes such as those described by theoretical science

How can experience non-directly justify beliefs of these kinds?

∀b (Jeb -> Jl

(b1&b2&…bn) -> b), where Jeb = a belief justified by experience and Jlb is belief justified by logically

prior reason

P1: Experience (e) can indirectly-justify (IJ) a belief (B).

P2: If P1, then (b1&b2…&bn) -> B).

P3: (b1&b2…&bn) -> B.

C: IJeB

Here, b1, b2,…bn are propositions that are directly justified by experience.

The argument depends on the truth of the conditional (P3). Why should we assume its truth? If B can be

reduced completely to the conjunction of beliefs that are directly justified by experience, then the

conditional is directly justified by experience. However, if B is irreducible to the conjunction and is over

and above the conjunction, then B cannot be directly justified by experience. Given this, it follows that

the conditional is justified a priori. Otherwise, we have no reason for thinking that any empirical claim

that is not directly justified by experience is true. (This seems an extreme outcome to BonJour).

2nd argument for a priori reasons

P1: If {(p->q)&p}->q (P), then there is a good reason for thinking that a conditional claim is true (Q).

P2. Q cannot be established by experience.

P3: Q can be established by another argument (conditional in form, involving transition from premisses to

conclusion), but this doesn’t answer the issue—what establishes the truth of the conditional claim? Only

leads to further regress.

C: Q can only be established a priori.