Once we grant thoughts themselves an ontological status, the next question becomes, can we apply objective criteria to the claims expressed by these thoughts? — Read Parfit
I'd point out how this all stems from analytic philosophy taking a Newtonian view of ontology. And that sets things up for an odd dualism that is at the heart of your OP.
So the assumption is that everything ontic can be reduced to states of affairs - some collection of particular individuated things. And then all these things have simple Newtonian relations. Each is an element of reality with some inherent property. You have then a calculus of relations where each element affects any other element in a fixed, determined and mechanical way. It is a world of straight lines of action with no deviations possible.
And so it is a world of logical operations too. Happily for AP ontology, physics is computational. One state of affairs maps onto the next state of affairs in utterly predictable and deterministic fashion because all causality is merely syntax. There are laws that set the rules. There are elements with properties that have to obey those rules. And that's it. Get computing.
Thus AP ontology is dualistic. Physics and logic are mirror images of each other in that both are about syntax determining what is possible in terms of reality. If you have A, it is going to give you B - so long as you know the rule that applies to your world of elements.
This is why AP winds up in modal realism. Unicorns might not exist in our world, but they could have evolved in some other world with the same natural laws. So they are a definite possibility. On the other hand, solid gold planets are impossible objects in worlds with our laws. Their gravity would collapse them into black holes.
It all does sort of makes sense.
But also it doesn't. And
@Wayfarer is right to highlight how it is all about syntax, and semantics gets left out.
AP just really struggles with semantics - just as classical Newtonian physics really ended up struggling with its story of a world of concrete observables that left out any physical account of the observers making sense of their observations. Not to mention how Newtonianism created a mystery in regard to how the laws could exist in a fashion where they did determine every state transition of a collection of material elements. And the leaving out of the observers who discover the laws, and the manner in which laws might be properly real, were of course a connected problem.
So AP ontology leaves you with this weird thing where all that seems to be going on when a brain is having thoughts is some collection of physical events. You have a bunch of neurons "firing". Something energetic is happening at synapses. If it is energetic, it must obey physical law - the standard universal syntax of Newtonian physics.
But also - dualistically - the physical pattern of activity is being caused by a second logical syntax. There is some kind of computational program being run. The brain is doing information processing. The physics now just instantiates the pattern. It gives the software some hardware.
However - from the AP point of view - the story is still safely Newtonian. There is some system of rules in play which determine each step of any transition from one state to the next. The ontology is mechanical in exactly the way classical physics imagines ontology. So the logical level of reality seems to safely parallel the material level of reality in this fashion. And then AP tries to get on with business without mentioning the gap.
Syntax is syntax after all. And physics is treating the material world as a logical pattern - rule-bound computation acting on elements with predicates. So why not believe the reverse? All possible logical patterns could be materially real. And so - in some sense - all logical patterns are real. If a brain imagines a unicorn or Pegasus, then that gives these individuals an ontological-strength claim to existing. They exist as a logical pattern in some set of circuits. The idea has happened materially.
Again, it sort of makes sense. Yet clearly, it is all rather out of whack. There is a dualism that is getting fudged. You have a realm of matter and a realm of form, with nothing properly connecting them.
In the Newtonian view, the laws provided the rules, and so the form of any material change. But where do these laws live? How do they act on the material?
In the computational view, the algorithms provide the rules, and so the form of any informational change. But why does it take such an atypical state of materiality to allow that to be the case? You just won't find computer circuitry appearing naturally in nature. A set of digital circuits wouldn't appear in any world just left on its own without the intervention of some human-scale imagination and a machine constructing culture.
A brain of course evolved. But brains are not machines or computers.
So we have this AP ontology that reduces existence to the syntactical. Everything is a logical pattern. Even physics - because, hey, Newton told us that back about 400 years ago. Thus to exist is this thing of being a material state of affairs - a collection of elements arranged in a pattern and deterministically controlled by a syntax. And then even a logical state of affairs exists as something real because it too is a collection of syntactically-controlled elements - that is thus always implementable as some material state of affairs. And so - the fudge arriving - the gap between the informational version of reality and the physical version of reality can be ignored.
Any blueprint for a machine could be turned into some actual machine. And thus the gap between the logical or informational, and the material or physical, is a fairly theoretical one that ontology can afford to ignore.
It sort of works as a rough approximation of reality. Both Newtonian physics and Turing computation are really great ... for building a world of machinery.
But science of course has moved on, both in physics, but especially in biology. And this is returning us towards a more sophisticated Aristotlelian "four causes" ontology. AP feels so last century now. You are dealing with a historical curiosity is all.