The Non-Physical
Parfit defends a narrow and wide ontological sense in relation to abstract concepts like math, truths and possibilities. Take the statement:
“(R) if it had been true that nothing ever existed, there would have been this truth.”
... and his conclusion...
“(S) though there would have been this truth, this truth would have existed only in the wide sense and the non-ontological sense.”
I am fine with this. I also think when we ‘discover’ these truths, these abstract concepts assume a new, if ephemeral, ontological status in the narrow sense, as physical patterns in our minds. These truths derive their power from accurately modeling how nature works, and help our minds ‘discover’ new possibilities. We sometimes take action to actualize these possibilities and thereby create other ontological entities, like an airplane. I believe this particular ontological transformation of abstract truths requires a conscious host.