I sometimes get asked why I take a priori reasoning seriously; after all empiricists should eschew such talk! Real empiricists do not engage the rationalist on their own turf…in true Type-Q style I should deny that there is an a priori/a posteriori or an analytic/synthetic distinction and deny as well that talk of possible worlds is meaningful. But I don’t.
Let us define A Priori knowledge as follows
APK=def justified necessarily true belief
Let us define A Priori justification as follows
APJ=def justification that is not based on experience (i.e. not based on sensing, perception, memory or introspection)
A Priori justification usually takes the form of a ‘rational seeming’ which phenomenologically is a kind of ‘seeing’ that something could or couldn’t be the case. One has an immediate intuition that the proposition couldn’t possibly be true (or false). So, for example, when I consider simple propositions like that A=A, ((P–>Q) & P) –>Q, and (P v ~P) <–> ~(P & ~P) I find it unimaginable that they could be false. It is this phenomenology which leads people to argue along the lines of ++
++ APJ –> APK
Since it seems to one unimaginable that P is false (or true) one concludes that it must be true (i.e. that it is necessarily true). It is also taken to be the case that the history of philosophy has demonstrated that experience cannot teach that something is necessary and so APJ is the only route to APK.
Now as an empiricist I want to deny that we have a priori knowledge but I want to allow there to be a priori justification. In other words I want to allow that rational seemings can provide justification even though they don’t provide (necessary) knowledge this is because rational seemings are, according to me, ultimately themselves dependent on how the world turns out. Suppose for the sake of argument that the above simple propositions are not in fact necessarily true. Suppose that they are just extremely well confirmed empirical generalizations. That is, suppose that the regularities of our Humean world regularly, and up until now reliably, provide us the kinds of experiences that justify instances of these propositions. Suppose further that you have organisms evolving in this environment. These organisms will likely develop systems that encapsulate these propositions. To these organisms these propositions will seem to be unimaginably false (or true) but they are not necessary truths (ex hypothesi) and they are ultimately justified by the organism’s ancestor’s experiences. But these propositions are true; it’s just that they aren’t necessarily true. So one can have knowledge that has a priori justification but that is not a priori knowledge. Now I am not here trying to give an argument for this view. I only mean to be pointing out that this is perfectly compatible with the empiricist view and so if one is careful one can be an empiricist and still think that we can have knowledge on the basis of a priori reasoning.
So far I have been only talking about knowledge of how the world actually is. Nothing has been said about the way it could be. reasoning about modality seems to me to be fundamentally rooted in our ability to imagine or conceive of various situations. Conceivability has traditionally thought to be a guide to what is possible and to be bounded only by what is contradictory. That this be true is certainly conceivable (just as is the empiricist version above). We may not know that it is true but it does seem like a possibility. So, for instance, it is almost impossible to see what it could even mean to say that [](A=A) is false…I mean that would have to mean that there was some thing picked out by ‘A’ which was identical to itself in some conceivable situations but was not identical to itself in other conceivable situations. That just intuitively seems contradictory! But, wait, we can have rational seemings in the absence of necessary truth. So, famously, when some people offered “proofs” of the parallel postulate they were accepted as correct until some mistake in the proof was discovered. If so, then there was a time when people could have a priori justification for something which turns out to be demonstrably false. So perhaps our intuition that justifies our belief in [](A=A) and the like are also suspect. As a counter example David Rosenthal talks about identity statements like [](A=A) beg the question by assuming the notion of rigid designation. If one doesn’t assume that it is of course not necessary. But it seems to me that the 2-D response has legs here: we can have both. Intuitions about rigidity are explained by the secondary intension and the corresponding kinds of possibility. Intuitions about the non-necessity of identities are explained by the primary intension and the corresponding kind of possibility. In short then as long as we see rational intuition as defeasible justification (defeasible in particular by experience) then we can accept the a priori justification of [](A=A) in the absence of defeaters which we have yet to find anyway
To sum up then; I think I can know that for any A, A=A a priori but not that [](A=A) yet even so I think that I have good justification for believing [](A=A) and []~(P & ~P) and so we have good justification of modal talk.
Richard Brown 
I fail to see your difference between „true” and ”necessarily true”. Of course we could go on about the Wittgensteinan-ish ”all that it is the case”, but that would’n fall under the category of justification, would it? And more the less under “rational” (supposing that rational seeming would lead to rational justification).
We can imagine worlds all right, but that doesn’t make “knowledge” (objectively) more or less justified by our impressions. Although, arguably, there’s always the psychological side of knowledge which is very tightly linked with seeming.
However, this is very un-Popper-ian, and I like it 🙂
I’m sympathetic to what you’re doing here, although I’m fuzzy on some of the details (especially re: modality).
One question I have is about why you don’t count a priori justified knowledge of contingent truths as “a priori knowledge”. I.e. why must a priori knowledge be knowledge of necessary truths? Of course we’re free to stipulate however we like here, but it seems to me that knowledge based (purely) on a priori justification is a prima facie good candidate for the title “a priori knowledge”.
Also, I’m wondering how analyticity figures in all of this. If you admit an analytic/synthetic distinction, then presumably your picture would allow synthetic propositions to be defeasibly a priori justified. Right? Or will you instead try to cram all a priori justification into the realm of the analytic?
Finally, do you know of anybody in the literature who treats rational intuitions as defeasible justifiers? I think one can read Bealer in this way, if I’m remembering correctly. Eli Chudnoff also has some cool stuff on “intellectual seemings” (understood phenomenally) as basic, defeasible justifiers. Know of anybody else in this ballpark?
Hi Brian, thanks for the comment.
I put it a bit hastily in the post but I agree with you that a priori justified knowledge of contingent truths counts as ordinary knowledge. I was using ‘a priori knowledge’ to specifically mean necessary truth…sorry about the confusion!
I do admit a synthetic/analytic distinction and am happy with (defeasible) a priori justification for synthetic truths…one way of reading my story about the mind is as claiming that mind/brain identities are synthetic a priori truths; that pain is identical to brain activity is not something that we can tell by analyzing the concepts but when we find out that it is so we then have justification via a priori means to believe that it is necessary…I guess something like this is the reason that I refuse to be called a type-A physicalist. Phenomenal properties are picked out by how they feel, at least from the first-person and I am doubtful that we will be able to provide analytic definitions of phenomenal properties…
Finally, I do not know the literature in epistemology very well these days…these are just my thoughts on the matter…but I should do some research on this and see what’s what…
Argumentics,
Thanks for the comment, though I am not really sure that I get it…something is true if it is actually the case (but might not have been the case) whereas something is necessarily true when it must be the case.
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“Suppose that they are just extremely well confirmed empirical generalizations.” – I was with you up until this point. It seems to me that this assumption alone sidesteps the whole issue. If a priori justifications were assumed to be empirical to its core, it wouldn’t be a priori at all. A priori is the explicit opposite of a posteriori.
Furthermore I’m having a hard understanding if you’re arguing against the synthetic or analytic distinction. I am getting a sense that you may have committed an unintentional obfuscation of the two and included them both in your definition of a priori. Which is strange since you acknowledged synthetic/analytic distinctions in the first paragraph and try to argue considering an a priori point of view. But to me there is a hard distinction between analytic a priori truths (which encompass the realm of definitions and subjective concepts) and synthetic a priori truths (which would tell something objectively true). Both are necessarily true, one from the very definition of itself and the other being from real things.
I’d like to know your take, because I am honestly confused by this article.
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