there is a fundamental reality

North,

Consider this.

Billions of dollars are being spent at CERN (the particle accelerator site) to try to account for what we call "mass", or what the layman might call "stuff" or "substance". That means that the use of the term "fundamental" as in "fundamental particles" is relative to particular experimental procedures, and theoretical explanations, but is in no way the "last word" with respect to what we call "reality". To understand the philosophical implications of this you simply need to ask whether there can ever be a "last word", and you can trace a "no" answer from at least as far back as Kant.

This is why your original statement "there is a fundamental reality" which you specifically couched in physical terms is either vacuous, or a matter of belief.

Now as JLN and I have indicated, there may be a level of awareness or vantage point, from which the vacuity of statements such as yours can be "understood". That hypothetical and ineffable state might be termed "fundamental" or even "transcendental", but whether it is a matter of "greater depth" or "the bed-rock" of what might call "consciousness of reality" , cannot even be asked, because asking involves slipping out of that state to the level of usage of words..

(Note that the second paragraph is not required for your understanding of the first).

The only thing you are hammering at is that we (as animals who plan ahead) all operate as though there was a fixed reality independent of our physiology and interests. You appear to have no understanding that the "details" of such a reality are under constant revision and what may be universally accepted as functional " at one level is open to speculation at another level. For example, Newton's laws work at for macro-objects (as defind by us) at "normal speeds" but give way to relativistic laws at the micro-level and higher speeds. There is no theoretical limit to the potential need for this giving way.....i.e. there is no axiomatic bedrock on which we can ultimately rely. Such a position would involve a TOE (theory of everything) and general opinion was that even Einstein wasted his later years on that one !

Here endeth the lesson writ bold !

Stephen Hawking was originally a believer in the Theory of Everything but, after considering Gödel's Theorem, concluded that one was not obtainable.
“ Some people will be very disappointed if there is not an ultimate theory, that can be formulated as a finite number of principles. I used to belong to that camp, but I have changed my mind. ”
—Gödel and the end of physics, July 20, 2002

I see you are in your "blind guess" mode ! Such a useful phrase when you can use it that very same day in both a discussion of the practices of physicists and also arbitrary speculation on life after death. !

Certainly more interesting than the blind guess that there is "fundamental reality" inaccessible to our perception.

I don't understand. This division between perceptible reality and fundamental reality seems backwards. To any human being, the most fundamental aspect of reality is that it happens to us.
I do not see any indications that we should assume that reality is anything other than what we are perceiving. That is not to say that what we know and think we know has any relevance to anything or anyone but us.

All expansion of what we call "knowledge" depends on hypothesis generated observation..in other words "a hunch" or "a guess". There are no independent "data". You have no idea of how to descriminate between an "educated guess" and a "blind guess" unless you are steeped in a particular exploratory paradigm, and even if the "educated guess" yields supportive data ,that guess remains a "working hypothesis" subject to possible refutation at any future time by counter-example.

A good example of the problems with the word "guess"can be found in the proposal of Clerk-Maxwell's electromagnetism equations which were based on the assumption(=guess) of "an elastic ether" in which e-m waves could vibrate. The equations "work" to this day despite the fact that "the ether" was shown to be non-existent by the Michaelson-Morley experiment on the speed of light. This is also a good example of how the guess of an aspect of "a fundamental physical reality" ( the ether) was shown NOT to be a requirement for epistemological progress.

At the risk of being accused at "argument from authority", I would suggest you consider why Hawking ( an educated guesser of the first order) has come out against a concept of a TOE, and by inference the necessity of "a fundamental reality."

If it is a useless concept, then why even discuss it?

I am attempting to show you why your catch-all "blind guess mode" is an excuse for intelligent discussion.

Your approach the concept of "fundamental reality", which has has no pragmatic usage, is merely to use it as a prop for your "IS-ing" mode, and is therefore merely illustrative of the failure such intelligent discussion.

But there is at least the possibility this is all an illusion.

Yes. But then, if that illusion is what happens when our senses meet the objects and phenomena they can detect, then that illusion is reality.