The Nuance Underlying Being Existentially Dependent Upon Humans We have arrived at a point where a bit of summarizing seems needed. There is no argument that humans have rather complex thought and belief systems. There is also no argument than rudimentary thought and belief cannot possibly meet a complex criterion. So, it seems necessary for a couple of reasons to be able to parse out all complex thought and belief in the same terms that successfully parses the simple.
The first reason would be to maintain consistency/coherency while avoiding equivocation. It would be rather unintelligible if not all thought and belief had the same basic elemental constituents, and yet I insisted upon calling them all by the same namesake. I mean, all thought and belief must have something or other in common in order to qualify as more than just a language game akin to Witt's notion of game where the only thing all games have in common is that we call them such. Thought and belief are no such thing.
Games are inventions of humans. Thought and belief are not. The only commonality relevant here is that they are both existentially dependent upon humans. The remarkable difference is that games are created/invented by us, whereas human thought and belief is discovered. Games are existentially dependent upon both, our awareness of them and our existence, whereas rudimentary thought and belief is only existentially dependent upon our existence.
I also do not want to posit a bunch of what has been historically referred to as 'mental furniture'. Rather, if this is to have any bite, it must be able to effectively exhaust all those archaic notions. It must be able to provide a very basic level, upon which everything ever thought, believed, written, and/or spoken could arise from. It ought be amenable to many a conventional viewpoint, and even those which disagree with it ought be able to be effectively explained and thus exhausted by virtue of employing it. These are tremendous justificatory burdens. The method and language is crucial.
The terms used to parse out all thought and belief(simple through the most complex) must be talking about that which is not existentially dependent our awareness, but is adequate for providing a basic outline capable of exhausting the complex as well as the simple. In the OP the second group of things that exist in their entirety, things that we discover, includes this basic outline of what all thought and belief have in common. At their fundamental core level of irreducibility, everything ever thought, believed, spoken, and/or written consists of and is therefore existentially dependent upon physiological sensory perception, spatiotemporal distinction, and the attribution/recognition of both, causality and meaning.
I want to be perfectly clear here.
Those three things are not existentially dependent upon humans in any way whatsoever. That is, all human thought and belief consists of these. We can establish these things are happening with other creatures too. Given that we already know that we were not the first creatures on the planet with the biological make-up required to accomodate these things, it only follows that they are not existentially dependent upon us in any way whatsoever. Our own thought and belief is most certainly existentially dependent upon us. The mechanisms for how it arises within us are not. Those are the basic mechanisms of all thought and belief. All thought and belief consists in/of these things. The differences arise in levels of complexity. The basics remain unchanged.