Metaphysical rationalism
My argument that the past must be infinite relied on the defining principle of metaphysical rationalism, namely the Principle of Sufficient Reason (PSR), which asserts that there’s a logically sufficient explanation for everything. Philosophers have long debated PSR, some accepting it and others rejecting it. Why do I accept it?
Not because there’s a purpose to everything. Far from it! Plenty of things exist on purpose ‒ this post, for example. But for reality to make complete sense, the things that exist on purpose must have logically sufficient reasons that don’t exist on purpose. As I explain in section 2.5 of my book, it can’t be “purposes all the way down.”
Rather, I accept PSR because the alternative is unintelligible: a universe in which something can happen even though there was no particular way it happened. Such a universe contains genuine magic, which by definition can’t be fully understood. If something magical happens, not even an omniscient being can know exactly how it happened: at some point, there’s nothing to know. Again, see section 2.5 for why.
Some critics of PSR argue that it implies necessitarianism, the doctrine that every truth is logically necessary. As I’ll explain in a later post, determinism is very different from necessitarianism; the latter doctrine has fatal flaws. For now I’ll just note that the critics’ argument from PSR to necessitarianism fails. (Pages 97-99 of my book explain why.)
