A Priori Knowledge

Right now, I'm unsure about what exactly is Con's main issue with the proposed definitions as those definitions are how a priori knowledge and justification has been standardly thought to be. Con is welcome to provide whatever argumentation he thinks tells against this standard way defining a priori knowledge and justification in the next round. Seeing as I do not want to try to preempt Con and inadvertently attack a straw man I will let Con present his case first and then critique it. In the meantime, I will present two short arguments for the existence of genuine, a priori knowledge/justification in the rationalist sense. [1] The Argument from Examples The following argument proceeds from the thesis that there are certain pieces of knowledge that we have that do derive their epistemological justificatory (justification is a key component for something to count as genuine knowledge) force from sensory experience. There are numerous examples (anything ranging from moral propositions to propositions about causality) but I will focus only on two less contentious ones:(1) 2 + 2 = 5(2) Nothing can be red and green all over at the same time. I contend that once one has properly understood the concepts involved in these two propositions one can "see" or "grasp" - I do not mean "see" or "grasp" in a sensory sense, I mean "see/grasp" to be understood here as a rational insight or intuition - that the propositions are true. [2] Not only are they true - they are necessarily true. Meaning they could not be false in any possible situation. Even just seeing that these propositions are necessarily true provides strong reason to think that the propositions are known a priori for it seems impossible that they be known a posterori (i. e. they derive their justification from an essential appeal to experience). The reason for thinking this because sensory experience (ignoring external world skepticism) only tells us what is actually the case - it doesn't tell us what is possibly or necessarily the case. [3] For example, me seeing this computer I'm typing on only tells me that this computer actually exists; what it doesn't help me know is that this computer could possibly have not existed. It's also unclear how, if everything is known a posteriori, how we know that some truths are necessary truths. So, propositions (1) and (2) do not seem to derive their justifications for being thought to be true from any essential appeal to sensory experience. There are multiple ways for some to respond to these arguments ranging from (implausibly) arguing that the propositions are really, appearances notwithstanding, grounded in experience, or (implausibly) arguing that the propositions are really analytic. I have no way to know how my opponent will respond so I will leave the argument at this juncture for now. Argument from Experience [4]I will argue, perhaps somewhat paradoxically, that for us to be justified in making any inferences from what we directly experience a priori knowledge has to exist. So, for much of the a posteriori claims many take themselves to be justified in believing one can only justifiably believe in them only if they infer them from other directly experienced or observed things. And this inference involves an unavoidable a priori element. Some of these a posterori propositions would be: the existence unobservable entities postulated by science, the unobserved past, the uniformity of nature, unobserved objects in the present, etc. No one, I think, would seriously contend that the aforementioned propositions are directly experienced - they are very indirect experiential claims. Now, what could justify these inferences from directly experienced things to indirectly experienced things? It seems only the a priori can do the job. If one frames the situation as follows it becomes much more clear. Suppose that we have some conditional claim of the "if-then" form. As the antecedent (the "if" part) we have certain direct experiential claims and as the consequent (the "then" part) we have certain indirect experiential claims. Obviously, the conditional goes along the form of "if [certain direct experiential claims are true] then [certain indirect experiential claims are true]. " The particular claims don't matter - what matters is that the inference has to be justified or else it isn't a good inference. Which type of knowledge could justify this inference? It seems that it can't be the direct experiential knowledge because all of that is already in the antecedent so the consequent goes beyond direct experience. It can't offer any justification for thinking the consequent is true (either direct or indirect) unless if the inference appeals to some justification that itself doesn't get it's justification from sensory experience. In other words, the a priori. If one denies the a priori one is denying that we can ever make good inferences from direct experiential claims to indirect experiential claims. This seems to be an incredibly implausible form of skepticism considering so much of the a posteriori knowledge we take ourselves to have is indirect. So we have good reason to believe in the existence of a priori knowledge/justification because rejecting it leads to an unacceptable amount of skepticism. Sources-----------------------------------------------------------------------------------------------------------------------------------------------------------[1] . http://plato.stanford.edu...[2] . http://plato.stanford.edu...[3] . http://plato.stanford.edu...[4] Matthias Steup and Ernest Sosa. Laurence Bonjour, "Is there A Priori Knowledge? ", Contemporary Debates in Epistemology, pgs 101 - 103