I think Kennethamy is on the right track trying to clearly set apart the differences between the definitions involved. I do not think he is being very precise though so I am going to follow his lead.
argument is based on the thought that everthing must have a beginning; a first mover of sorts (as Aristotle ment it). No obeservation is neede to make it. It is metaphysical in nature. I think the referral that is made in this topic is to pantheism
, but I may be mistaken.
argument is based on the thought that for reason (or actuality) to be possible "something" must have created it ("God"); something must have "created it" ehich must have "come before".
The difference between pantheism and the ontological/cosmological arguments is almost the same as between rationalism and empiricism:
is the philosophy that states thought begings with perception. From these perceptions thought-objects are formed and with these thought-objects we can start thinking.
This would form a problem for empiricists for the first thougt-objects to be formed because without thought-objects there can be no thought according to empirism. Rationalism has a solution for that.
is the philosophy which states that for thought-objects to be formed we must understand (at least at some level) what it is we are percieving. There is some "a priori" knowledge necessary to form thought-objects. This a priori knowledge is the most basal knowledge of time and space. According to Immaluel Kant this a priori knowledge of space and time consists of his "categoria".
So, where the problem for an empiricist, as kennethamy stated, is:
how could a person ever arrive at such knowledge, and how could a person ever confirm that such an a priori proposition was true. How would he be able to justify such a proposition?
The question for a rationalist would be:
How can one arrive at knowledge if no knowledge is present to help one understand what we percieve.
This argument assumes that thinking is causal in nature and therefore needs comparing. Until now I have never seen an argument against this apart from empiricists who confuse conclusions they do not conclude themselves with irrationality.
Anyway, to get back to your post "a priori" knowledge points to the
thing-in-itself and not to what we percieve.
Hope this helps.