Quine has helped me better understand why we should reject a priori as a valuable concept at all.
It seems that most examples of a priori justification can be explained by language and semantics.
All bachelors are unmarried males.1
The classic example of a priori justification is a synonym.
In order to understand this sentence, one must have prior knowledge of the definition for these words. They must also understand the structure of a sentence to fully grasp its meaning. The proposition requires knowledge from experience.
Further, as a thought experiment, let's say we traveled to the future and looked up the definition of bachelor and it comes to mean someone who is married (the opposite of its current definition). Does that not reject the a priori statement based on experience? The whole idea seems like a semantic game that provides little value for knowledge. And yet, so much mental labor has been devoted to comparing a priori and a posteriori. This is a distraction.
I would also argue that without the reader, this statement cannot be understood. A reader must read the statement, which requires time and space -- both of which fall under the category of experience. All justifications must necessarily require experience because they require space and time in order to read and understand them. Like Kant, our world is perceived through the lens of the human mind. Propositions, justifications, and knowledge also require the human mind. The statement and the reader cannot be sufficiently separated.
After Quine dropped a bomb with The two dogmas of empiricism, it seems we have moved the goal post from Kant's definition of a priori:
knowledge that is absolutely independent of all experience2
To a definition that is a little more lax:
"independent of experience" should not be taken to mean independent of all experience, but, as a first approximation, to mean "independent of all experience beyond what is needed to grasp the relevant concepts involved in the proposition".3
When reading this modified definition of a priori I cannot help but ask: what is the value in making this distinction? What value do we get from understanding justifications prior to some types of experience and a posteriori?
Let's look at a mathematical example of a priori justification
2 + 2 = 4
Let's just say for a second that a priori is legitimate and this is a good example of one. What do we gain from this information?
I could go deeper into the mathematical example but it's been awhile since I've thought about the philosophy of math and logic.
Kant, Immanuel, 1787 , Critique of Pure Reason ↩︎