Otherwise, what are we to make of the secular belief in, say, future scientific progress? Is that not a belief in an unseen future state of things? Does it therefore amount to "blind faith" to believe in such a future? I propose that most reasonable people would say that no, it does not, because that belief in the future amounts to a sort of extrapolation, however vague and precarious, of a trajectory of history for which we have plenty of evidence.

And so similarly, when Paul says that we "walk by faith, not by sight", it is because he "already has the Spirit as a first installment". That is, he has already experienced something that justifies his faith. This is the very opposite of blind faith. The most immediate form of knowledge possible, direct personal experience, has endowed him with a hermeneutic key to history, a history that he can therefore extrapolate, however vaguely and precariously, into an unseen future. He is walking toward that future with a justified faith, not a blind faith.

With John 20:29 something slightly different is going on, although it's still in the same general zip code. Jesus is chastising Thomas because he has insisted on a miraculous display of divine power in order to underwrite his trust. There's nothing wrong with asking for evidence, but it would have been a greater blessing for Thomas to perceive and trust the centrality of Jesus without the benefit of the whiz-bang pyrotechnics. A real, healthy trust in another person is a trust that, while inquisitive, does not insist on the other person's complete self-revelation.

Yes, I am a Christian. In orthodox Christianity, fideism is verboten.

Now go ahead and tell me why you think that is inconsistent with Christianity, as you could have done earlier.

No, of course I don't think blind faith is good way to determine anything. I don't advocate blind faith at all.

(???)

As far as blind faith ... I think what people generally mean by that is something like "believing something just because someone told you so, without the benefit of any corroborating evidence". Of course even that is not exactly blind: presumably you accept someone's say-so because that person has earned your trust, i.e. you can reason from the evidence to conclude that that person is trustworthy.

But in any case, that is not the essence of the point I was making. The point I was making was that faith and reason (again, inductive or otherwise) cannot be disentangled, unless one is engaging in a purely mathematical type of reasoning and bracketing all questions of applicability to reality. Faith and reason lean on each other for support. Inductive reasoning requires implicit faith in the continued coherence of reality.

Then at some point of maturity, around college age IIRC, I began to reflect on the nature of this faith, and to consider whether I could do without it. And there are, of course, practical arguments in favor of faith in inductive reasoning, such as wanting to avoid a life of paranoid anxiety about the future. But arguably that is neither here nor there with respect to epistemic warrant: just because something makes you paranoid and anxious doesn't mean it's not true. So, it seemed to me that there was something deeper than mere pragmatism going on. And eventually I found myself with the position that I still have to this day: there is something at the deepest depths of reality that I trust, and that's that. Belief in inductive reasoning is a fruit of, or an aspect of, this "deepest faith". Any rational analysis of my "deepest faith" will itself be founded on my "deepest faith", so I'm afraid I don't see a way to dig any deeper.

The problem with this is if the PSR is not true, then it is equally possible that your very belief that the PSR might not be true has no sufficient reason for existing.

Maybe, but one cannot infer “We should believe it” from “It’s possibly true.”

Therefore, it would be irrational for me or anyone else to take that conjecture very seriously.

Yes, if your only reason for taking it seriously was my asserting it. But rationality is about the exercise of reason, which among other things is about logical consistency. If the PSR is consistent with your worldview, then it is rational for you to accept it. If its negation is consistent with my worldview, then it’s rational for me to think it’s possible that the PSR is false. There are some things that rational people can disagree about, don’t you agree?

How do we know that there is rational and sufficient reason for your belief...we don't know and neither would you.

The PSR makes an assertion about all of our beliefs. To deny “For all X, Y” is not to affirm, “For no X, Y.”

If the PNC is merely a logical abstraction, would you then claim it is possible for you to exist and not-exist at the same time, in the same place, and in the same respect?

I would claim that without the PNC, such a statement could not mean anything, and that any meaningless statement cannot be either true or false.

If I remember correctly, you did say that you take the capability for good reasoning towards truth as a first principle, or assumption in your philosophical system. A first principle in a philosophical system gets at what is most true and evident because it is that which everything else is built upon.

I don’t agree that our assumptions are about things that are “most true.” Strictly speaking, truth doesn’t exist in degrees. Probability does, and we have to be careful about thinking that “more probably true” is a way of saying “more true.” And we should never think that just because we justifiably assume something, we can assign it a probability of exactly 1.0.

We may well begin our reasoning, in some important sense, with our assumptions, but that doesn’t mean the assumptions themselves are forever off the table. We still learn about reality by observing it, and if we observe something that cannot be reconciled with one of our assumptions and if we cannot dismiss the observation as an illusion or other product of human fallibility, then it may be time to revise or discard that assumption.

What would be your first principle about reality if it isn't human reason capable of discovering truth?

I don’t have just one. My worldview rests on several assumptions, and I don’t rank them in any order. Besides, assumptions are supposed to be independent of each other. If my assumption B depends on my assumption A, then I’m not really assuming B. I am assuming A and then inferring B.

Just a few philosophical principles that science relies upon:

1) The scientific method itself (which isn't a scientific theory that can be tested and falsified)
2) Principle of causality
3) PNC
4) PSR
5) Intelligibility of external world
6) Capability of the human mind to discover truth

All of this depends on how you’re defining “science,” but in ordinary discourse, “scientific method” is just a description of how the people we call scientists do their jobs, and it serves as a means of distinguishing science, whatever we think it is, from all the other ways human beings have come up with for answering questions. We who argue that intelligent design is not science do so by claiming that ID’s practitioners do not actually comply with the scientific method.

The other items on this list are not unique to science no matter how we define science. Generally speaking, even people who are actively hostile to science accept them, and so if science relies on them, then so does every other kind of human intellectual endeavor. A possible exception would be (6), considering that there are people who deny our ability to discover truth. However, many who think we can discover truth also deny that science is the best way for us to do it.

we need to ask, okay, what philosophical principles must be true if science actually works as we are finding it to work.

That is what philosophers of science have been trying to figure out for the past century or so. Last time I checked, they hadn’t reached a consensus, but I don’t recall any of them offering the PSR as any part of their explanation.

But to head back towards our main discussion of what could completely explain and account of the intelligibly of the material cosmos and the ability of the mind to reason to truth.

If this discussion is attempting to reach a complete explanation, then I need to withdraw now.

Unfortunately, falling into an intellectual black hole is the penalty for anyone not holding the PNC or PSR to be true.

I have repeatedly defended my acceptance of the PNC. I am denying only that the PSR is necessarily true, and I am specifically denying that the PNC depends on it, and you have failed to show any mistake in my non-PSR-dependent defense of the PNC.