How does prolepsis help to disprove that “all this - including our thought processes - have been supernaturally created”? From what I understand, prolepsis just describes instances of in-built knowledge, right? But not where those preconceptions come from? Couldn’t a supernatural believer still just respond, “well those preconceptions come from god”?
It "disproves" a supernatural basis for thought processes by providing a rational non-supernatural basis for understanding what we observe to be the case in the way people think and make decisions, without resorting to pre--existence or other supernatural arguments. This is very parallel to atomism, which provides a non-supernatural basis for the way the world works. In both cases you're now asking how atomism or prolepsis/canonics "disprove" the supernatural, and the answer to that has to come down to your conclusions about what kind of proof is possible and what is required. If you fall into the belief that only god can provide certainty, then you can never meet that standard -- but there is no reason to accept that supernatural standard in the first place. This is an issue far beyond the prolepsis alone and falls under general canonics, but prolepsis is an important part.
Have I missed something? I tend to think that the prolepsis discussed by Epicurus was based on a limitation of his access to modern science 2,300 years ago. I think it is becoming clearer that a conception that you can know something before you apprehend it, or use your senses to learn it, is not how we know things.
Others may agree with you DaveT, but speaking only for myself I don't think Epicurus would have cared any more what science today says than we should care about what science in 4500 AD will say. We can only live our lives with the information that we have. Epicurus knew that using the word "prolepsis" does not convey all the details of thought, just as he knew that talking about "atoms" doesn't explain all the workings of the human body.
It seems clear that prolepsis was considered to be an advanced topic, and that's why it is not explained at length in Epicurus' letters or in Lucretius.
As to "a conception that you can know something before you apprehend it, or use your senses to learn it, is not how we know things" I don't think that this gets to the heart of the issue. I think the best way to get to that is to read some of the material on the Meno paradox, as that sets out the logical dilemma that Plato was trying to throw in the way of any philosophy based on the senses. To me the prolepsis issue is geared toward that debate, and I suspect that it leads to a lot of spinning wheels to read something "clinical" into it that will improve day to day pleasure/pain decisionmaking.