priori justification, differentiate it from a posteriori justification and see where each fits in the context.
As such, following an excellent essay on the item, a priori knowledge refers to a proposition that is "knowable independently of experience"
, as such, to nonempirical knowledge. A priori justification then refers to a justification that is not dependent on experience, that is either known to be so (as in the case of an axiom) or that has a reason not related to direct personal experience.
In order to properly suggest the difference between the a priori and a posteriori justification, it is best to give out some examples. As such, "examples of a posteriori justification include many ordinary perceptual, memorial, and introspective beliefs, as well as belief in many of the claims of the natural sciences" and may include things like the neuronal cells are not regenerating, cloud may lead to rain or Christopher Columbus discovered America.
On the other hand, a priori justification is related to examples such as the sun is yellow, "if today is Tuesday then today is not Thursday"
or the axiom that two parallel lines never meet (instinctually, I assume that two parallel lines never meet, because it seems natural to be so). As such, we already have a differentiation between a priori justification, where reason intervenes, and a posteriori justification, where we base our assumption and statement on experience, either our own or that of others.
Because a priori justification seems to be more directly linked to thought and reason, it seems natural to assume that rationalism is the strongest position we may have on rationalism. Here, we differentiate two different trends: continental rationalism and modern rationalism
. The former has its roots with Rene Descartes's teachings in the 17th century and his famous statement "cogito, ergo sum" (I think, therefore I am). Continental rationalism best applies in our discussion on a priori justification.
To the notion of continental rationalism, which is rather a current than the actual philosophical argument, we should also add the concept of rational insight
. In my own opinion, rational insight comes quite close to the philosophical representation of an axiom and here I have to use the example with the parallel lines again. According to my reasoning and the way I visually and mentally perceive the concept and notion of two parallel line, these lines must (and in the case of a priori justification, the must is a necessity) never meet.
However, such an expose may lead to a strong argumentation either disfavoring a priori justification altogether or proving that rationalism does not necessarily support a priori justification. This has several explanations. First of all, we may always wonder whether an a priori justification is indeed correct, because the only argumentation we have in favor of it is that the statement must be true or false, because reason points out towards this. On the other hand, we know that things that can be palpably proven are more likely to be believed. We would believe alien exist if we could see or touch them. In the present, we may believe that they exist simply because our reason cannot conceive that in a vast and infinite Universe, no other forms of life exist.
Second of all, a rational position on a priori justification can be proven wrong at some particular time, again, because of lack of solid evidence, which seems to me the greatest disadvantage of a rational position here. What happens if someone proves that two parallel lines do meet at some point in the future? Can we believe that such a proof would exclude, in the future, argumentation based on the fact that a rational perceiving of facts and that a thing must rationally be so will no longer stand?
Summing up the argumentation on rationalism and a rational position in the case of a priori justification, we may state that such a position best applies because of its strong bond with the actual definition of a priori justification. The fact that a priori justification relies almost solely on reason and on the logical perception of the veracity of a statement makes me believe that a rational position is the strongest position on a priori justification.
I tend to rule out from my two choices radical empiricism, following the thoughts of K. Ajdukiewicz on it. In his book, he defines radical empiricism as a "thesis according to which only empirical sentences may have scientific status"
. The reason I do not find radical empiricism necessarily explaining a priori justification is that it refers to scientific status. What about a statement that has a priori justification, but does not necessarily involve a scientific status? We can certainly believe that, while on one hand, the fact that two parallel lines never meet cannot be proven empirically (although we may assume that drawing two parallel lines around the globe would prove our statement), the fact is nevertheless true and we perceive it as such. Discussion may also come to Husserl and his phenomenological theory, however, we should not go into details.
We come to discuss now skepticism and moderate empiricism. According to an opinion to which I subscribe, "that it fails to explain why rational intuition and phenomenal experience count as basic sources of evidence"
. This I have already previously mentioned when I have referred to radical empiricism and the idea still stands here: intuition is to be taken into consideration when judging an a priori justification and, in my opinion, the basic definition of an a priori justification takes us to intuition, as we assume something must be true without proof of it.
I need to briefly bring into discussion Casullo and his excellent book on the subject of a priori justification. His definition points out that a priori justification is "just nonexperiential justification"
. Even if questions arise from Casullo's book and explanations, I will tend to go along with the idea that a priori justification does not go hand in hand with empiricism of any nature.
This leaves skepticism, which in my opinion, best goes along with my first choice of rationalism. I will only briefly refer to Descartes's view on the subject, even if Descartes rather refers to a priori knowledge rather than a priori justification. According to him, sitting at the desk and seeing a blue cube in front of you on the table may not be sufficient reason to believe that the blue cube is actually there. Indeed, this is something our senses may perceive, sight and perhaps touch, however, at that certain time, we may be hallucinating or may have lost our sensorial capacities, which would mean that our a priori justification on the existence of the cube is entirely false.
Skepticism comes to oppose empiricism, not necessarily because it brings a different argumentation for a priori justification a different position, but because it denies the extent to which justification may rely on the senses, on empiricism and experiments and, as such, weakens the role of the experimental in a priori justification.
Further more, in my opinion, skepticism opposes empiricism in a posteriori justification as well, following the same logical train of thoughts I presented in the previous paragraphs.
As such, we are able to draw a conclusion on the findings in the essay. According to this, rationalism and skepticism tend to be the two best positions to support a priori justification. The strongest argument in this sense is the fact that a priori justification relies on intuition and initial reasoning, with experimental or sensorial proof. Something which we know it must be true cannot work hand in hand with experimenting and proving that it is indeed true (a posteriori justification). Skepticism does not necessarily support rationalism, but it undermines the empiricist point-of-view…