Hypothesis: Physics and mathematics are those discourses in which Nominalism involves no immediate contradiction.
By “Nominalism” I mean the claim that predicated natures are beings of reason.* When we say “John is a man” then the predicate can be viewed without immediate contradiction as an ens rationis, abstracted from the concrete reality of “John” or “this man”.
But there is an immediate contradiction in assuming the same thing about “John is real” or “a being”. The real is divided by contradiction from the unreal or the being of reason. One is free to see “being” or “real” as the limit of abstraction, but the limit is not homogeneous with what leads up to it – at the most general level one hits something that does engender a contradiction if it is seen as merely logical, abstract, or ens rationis.
But to leave it at this would give us the universe of Parmenides. Being is common to all and so undivided; if it is real, then all is undivided, i.e. one. For the same reason, all beings are alike and the only possible source of difference is non-being – but this is the same as saying that there are no differences at all.
To explain the world we actually find, however, where there are beings – we need to say with the Manualist tradition that being is transcendent, that is, being is limited neither to the abstract nor the concrete; and that it is equally a source of likeness among all things and also the differences we find among them.
What is fascinating about this is that it requires that subsistent being would be at once abstract and concrete – that is, both like an abstract Platonic form or natural law and like a person; and it predicts that subsistent being would be at once completely unified and differentiated. The first claim is the only way one could satisfy Plato’s problem with how God could be worthy of worship (i.e. The Euthyphro dilemma); and the second is a doctrine that has only ever been advanced by Trinitarians.
This includes both Nominalists strictu sensu and Ockhamists and the various other Medieval Conceptualists. It also includes all those Aristotelian-Thomists who try to be “moderate realists” by placing the universal ante rem in the mind of God. If anyone cared to ask me, I do think this position is just Nominalism.