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What I think I know

  • A priori knowledge that can be gained by contemplating only the meaning of a statement's words.
  • A posteriori knowledge can be gained only by comparing a statement's meaning with the state of affairs.
  • Analytic knowledge that can be gained by contemplating only the meaning of a statement's words.
  • Synthetic knowledge that is not gained analytically

The problem

I understood the definitions of 'a priori' and 'analytic' to be extensionally identical. The definitions of 'synthetic' and 'a posteriori' that I used here may be different, but I'm doubtful - as it seems to me that there are only two ways of verifying a statement: deduction, and induction. From what I (probably, incorrectly) understand, 'A priori' and 'analytic' refer to 'deduction'; this leaves 'synthetic' and 'a posteriori' to share 'induction'. Yet, people who know more about philosophy than I know about it, and who have thought about these terms more than I have thought about them, seem to be able to distinguish between the two sets of terms.

The question

What distinguishes 'A priori' from 'analytic'?

What distinguishes 'synthetic' from 'a posterior'?

Thank you

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The definition of any of these terms is going to be controversial, but your first problem is that your definition of a priori is wrong. The traditional definition is "knowable independent of (any particular) experience". Now, analytic truths (traditionally conceived) are a priori knowable, but just because the analytic truths are a subset of the a priori truths doesn't muddy the distinction.

Regarding "'A priori' and 'analytic' refer to 'deduction'; this leaves 'synthetic' and 'a posteriori' to share 'induction'." There is certainly no reference relation between any of these terms. You might think that the means to uncovering a priori or analytic truths is typically deductive whereas the means to uncovering synthetic truths is typically inductive. But you can reason deductively about synthetic truths (this happens whenever you give a deductive argument with synthetic truths as premises) and likewise for reasoning inductively about a priori or analytic truths.

Quine's "Two Dogmas of Empiricism" is the locus classicus for criticism of these distinctions. Kripke rehabilitates a few of them in Naming and Necessity.

See the following two SEP articles for more general information:

The a priori

Analytic/Synthetic

  • Re: a priori - 'knowable independent of any particular experience' would be reasoning with, and drawing a conclusion from, the facts a subject knows at the time he begins reasoning? Aside from that and experience, how else could a person attain knowledge? – Hal May 26 '13 at 5:34
  • @Hal This question is exactly the import of the "any particular" parenthetical. Plausibly you need some experiences to form concepts and develop your capacity to reason. It's not the facts the subject knows at the time s/he begins reasoning. Rather, it is reasoning from facts that didn't require some empirical investigation to uncover. For example, I couldn't know a priori that our solar system has 9 (well, I guess 8 now) planets. I could know that everything is self-identical, however. Now this might not be too great an example because the explanation of how I could know that a priori... – Dennis May 26 '13 at 6:10
  • ...might just be that it is analytic--- that just is part of what identity means! Some philosophers think that the two categories are co-extensive, that every a priori truth is an analytic truth and vice versa. I'm afraid that I don't have a good example of some truth that falls into one category but not the other. I linked to two SEP articles in my edit, they might help along these lines. – Dennis May 26 '13 at 6:17
  • That everything is self-identical is a rule of thought that says something about how a thinker thinks about things, but doesn't a thinker need some content for his thoughts? If he can not obtain that content through experience (even if his experiences are limited to his own introspection), then how else could he obtain it? [I will read those links] – Hal May 26 '13 at 6:45
  • @Hal I want to try to avoid turning the comment thread into a discussion, but the idea that "rules of thought" and analytic truths have no content is an idea that goes back to logical positivism and is tied into a verificationist theory of meaning. Verificationism about meaning is widely (unanimously?) thought to be debunked. These two links will give you more info on that school of thought: The Vienna Circle and Logical Positivism. – Dennis May 26 '13 at 6:57
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The difference between the realm of a priori / a posteriori and analytic / synthetic is that that one is an epistemological notion(acquisition of knowledge) and one is a semantical notion (definitions of words). The a priori / a posteriori distinction tells us whether we know something by sitting in our armchair and thinking about it (a priori), or by going out into the world and look/feel/smell things (a posteriori).

The analytic / synthetic distinction tells us on what grounds something is true. If a sentence is analytic (and true), it is true in virtue of the meaning of the words. If it is synthetic and true, it is not true in virtue its words.

What distinguishes 'A priori' from 'analytic'?

A lot of philosophers thought that whatever is a priori (can be known without observations) is also analytic. I know that all bachelors are unmarried, but for this I need not go out and look at bachelors and do a survey whether they are unmarried or married. Mathematical truths are thought to be a priori and analytic as well.

According to Kripke, a statement that is analytic and not a priori is this: Water is H2O. It is analytic (Water just means H2O), but we need observation to get to know the truth of it (which makes it a posteriori).

What distinguishes 'synthetic' from 'a posteriori'?

Here is a statement needed, that is a priori and synthetic. Something that is knowable without looking into the world, but whose truth depends upon things outside the meaning of the words in that sentence. There are philosophers who think that there are those statements, but as far as I know it is nowadays thought to be a category that is empty.

As Dennis mentioned: All this is under heavy discussion and there are a lot of questions around the different notions, so take this answer with caution (There are those who claim that a priori and a posteriori does not cut at the epistemological joints and should be abandoned, there are those who say nothing is a priori, and so on).

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