Finding a word to describe that which is fundamentally real

Question

I'm trying to articulate my perception of reality for a blog post. Core to the clarity of this post is that it successfully transmit a certain very deep and abstract notion. I struggle to convey this notion in all its depth; the best I can do is approximate the intellectual dimensions of the idea. I want the reader to appreciate the full spectrum of depth and meaning of the idea and to appreciate its emotional component too. And that's why I'm here.

The notion I'm trying to convey is as follows. Suppose you have some system of thought. Within this system, there are things which it considers to be real, true, fundamentally deep and meaningful, founded in absoluteness, that is, part of the fundamental structure of the system itself and not synthetic, constructed, subjective, or arbitrary. These objects whether they be physical or purely intellectual space, are the most real things that can exist in their systems. For example: gravity, pure mathematics, a certain way of life, etc.

What would be the adjective to describe this form of realness

Answer 1

How about elemental.

https://www.merriam-webster.com/dictionary/elemental

of, relating to, or being the basic or essential constituent of something

As its root "element" implies, the word describes things or concepts which are the building blocks of more complex, "synthetic" constructions. Just like every substance on earth is made of basic "elements" in Chemistry, elemental concepts and objects are "underived," and form the basis from which complex or subjective constructs are made.

Answer 2

Given that you already seem to like it, just go with fundamental.

Ontology is the philosophical field concerning what is really real and epistemology is the related one for how to learn about it, but as far as the bedrock stuff you believe that you've found or established by using it... well, there's a horde of them—fundamental, elemental, essential, inherent, bedrock, primary, initial, base, basal, basic—but they're all generic and you're going to have to add your ontological flavoring to it in your introduction anyway.

As @Stevesliva already noted, the gold standard of ontology are self-evident, self-proving, self-verifying, obvious, &c. creations of logic that are obvious to any rational agent. The problem is no a priori truths have been found that people can agree on once you separate police power from the religious authorities. (We thought set theory was going to be able to tie everything up into a nice bow but ran into Gödel's Paradox. Now, we just accept that empiricism produces better societal results than the other options and periodically make movies like the Matrix or Waking Life.)