I think of metaphysics as akin to poetry. If you can’t ground arguments in empiricism and experience, you can’t really say with certainty whether what you’re claiming is in fact true or merely clever.
So my first argument against metaphysical philosophy of the Thomistic sort is that it is poetry. It’s a way of framing the world; of narrating it; of making some parts of it central and seen, and other parts marginal or not seen. This is what poetry, especially epic poetry, does.
And this is fine if you aren’t under the spell of your metaphysical system. But when you translate your metaphysics into dogma, you’ve stopped taking your poetry with a light touch, and you’re now in the realm of treating your deductions and system with 100% certainty. This is akin to the way a fundamentalist reads the Bible or Quran. The system is impermeable to reality testing even in principle, and you believe it 100%.
But this is folly because of our existential situation. We are evolved primates on a tiny planet adrift in the vast ocean of space. We necessarily inhabit the realm of probability; a realm of fog; of life “beneath the moon” (the sublunary).
Shakespeare, for this reason, is a better philosopher than Aquinas. And even Charlton Heston gets closer to the truth than Aquinas in the 1960s version of Planet of the Apes (“It’s a mad house! A mad house!”).
Camus is also superior to Aquinas. The cosmos is absurd from our vantage; it does not answer to human longing. But Camus tells us that we still have solidarity and rebellion against the absurd (making collective and private meaning for ourselves). Camus’ The Plague is a better guide for living than Aquinas’ Summa.
And we’ve got reason as a tool to help us along. We know, for instance, that if the premises of a deductive argument are true, the conclusion is 100% certain. That’s a great tool to have for coming at the world. But it’s often difficult to know, absent experience and empiricism, whether the premises put forward in an argument really are true. And this means that a philosophical system that cannot reality test even in principle is akin to speculating about how many angels can dance on the head of a pin.
My second argument against Thomism is that it pretends to transcend history. For example, I think it’s quite obvious that the starting point for Thomistic reasoning about sex is a contingent historical byproduct of an age in which maintaining population size was difficult and the priests writing the laws of sexual conduct were sexual innocents themselves (and all male). Rather than procreation, Thomistic philosophizing about sex could be started with love and (gender and orientation) equality.
So what Thomists don’t seem to acknowledge is that the premises from which their reasoning proceeds is historically situated. Aquinas started his project as an attempt to escape the contingent and transcend it with an act of pure reasoning. He appealed to divine authority (the Bible, etc.) absent experience, and this was an early mistake.
I like the way Bertrand Russell contrasts the theologian with the scientist in his A History of Western Philosophy (1945, p. 517 in the 2007 Touchstone edition): “[I]t is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition.”
I’m with Russell.