Our conception of logic, as I described to Alan, is what evolved in our ancestors and even developed in us in our childhood. Without any inkling of logic (P1) would be meaningless.
Looking at the acceptance of logic from the perspective of sitting here at my keyboard and computer (i.e., ignoring evolution and how my memories of how my conception of logic was inbred as a child), I see that I am naturally drawn to certain conclusions. Why I have those natural conclusions (or logic) appears to me as inbred within me. If I try to imagine an illogical thought (e.g., I am not at my keyboard typing right now), then I my actions are not meaningful when compared to that illogical thought. The only meaning that I can grasp of the situation is what I see as being logical (i.e., from my memories I recall that this kind of thinking is logical). Hence, in order to continue meaningful (i.e., in relation to my perceptions and memories), I must elect to accept this logical framework. [Of course, looking at this from the perspective of my knowledge of science and philosophy, I am drawn to the conclusion that logic is an evolved feature in humans that is further refined in childhood - which is why I experience logical thinking as the only meaningful experience].
***The standard reply to that complaint of mine is, "well, who says the universe is logical". To which I can only say, "that has nothing to do with it". And we are back to square one.***
The key is what is meaningful to us. However, we shouldn't kid ourselves either, if we have strong pragmatic reasons to believe that our way of thinking is the working order of the universe (e.g., the universe is mathematical), then we shouldn't be afraid of making this conclusion. We cannot be sure that this conclusion is correct, but we have strong reason for believing it to be true (just like I have strong reason in believing that I am sitting on a chair right now). Could be wrong, but I think not.
***That is, whether you are "here" experiencing all this stuff or "in a vat" being fed memories is an entirely meaningless question as there is no difference at all between the two scenarios. If there were any difference you could know about it! The fact that you cannot know, and you have said that yourself, means the two are in fact the same thing!***
Maybe I cannot convince you, but for the record I think you are wrong. If our conception of truth is so distorted that we cannot be right on something as trivial as us being 'here', then the concept of human truths in anyway equating with real truths of the world is completely overthrown. If we knew this to be the case, then the post-modern pragmatic subjectivists (e.g., the philosopher Richard Rorty) are much more correct than we can imagine. This should affect our philosophy of science and philosophies in general quite dramatically (as witnessed by the philosophy of the post-modernists). True, we cannot prove people like Rorty wrong, but proof is not the key issue - it is what we believe to be true is the key issue. It is vital, in my view, that we view post-modernist pragmatic philosophy as wrong.
***The major difference between us, as it has become apparent, is that you think you know absolutely nothing for sure while I maintain that if that were the case this conversation would be impossible. The fact that we are having this conversation is proof beyond any doubt, reasonable or otherwise, that we know many things for sure. Let's build our knowledge on that!***
I disagree. I think you are confusing 'believe very strongly' with 'know very surely'. I believe very strongly that pragmatic realism is right. Whereas I do not 'know very surely'. I know nothing very surely - i.e., in a stricter sense of 'knowledge'. I have knowledge that is built on 'believe very strongly' beliefs (many I consider facts), but I also conclude from my 'believe very strongly' position, that any knowledge built from this position is vunerable to being wrong - despite all that I 'believe very strongly'.
Warm regards, Harv