I looked up the difference because I don't use those words in everyday life, and wanted to get a better understanding:
A priori and a posteriori claims are types of knowledge distinguished by how they're justified:A priori knowledge is independent of experience (e.g., math, logic, definitions like "bachelors are unmarried"), known through pure reason; A posteriori knowledge depends on empirical experience and observation (e.g., "it's raining," scientific facts). The former relies on thought, the latter on senses or data from the world.
I want to strongly agree with this comment. "A priori" and "A prosteriori" are certainly very useful terms in the right circumstances and of course thanks to Joshua for pointing them out. But as Kalosyni says, practically no normal person in real life uses these terms or anything close to them. Not that I am a good model for anything but they just don't connect with me even after years of reading them. I therefore think they aren't the best way to explain this issue to the kind of regular people who are the target audience of Epicureanfriends.com .
On the other hand the issue being discussed is of huge importance to our target audience. I am hoping we can continue to refine how we explain these issues without reference to Greek or Latin words which smack of "lingo" with which normal people will never be able to be comfortable.
This is maye the key distinguishing feature of what Epicurean Canonics is all about and we need clear and ordinary terms by which to explain it.