published on April 3, 2018
Why Did Aquinas Hold That Killing is Sometimes Just, But Never Lying?
Aquinas held that lying is always a sin, an evil action (ST II-II, Q110, A3). In later terminology it falls under what would be called an intrinsically evil action. Under no circumstances can it be a good action. Following Augustine, Aquinas held that even if others must die, one must still never tell a lie (ST II-II, Q110, A3, ad 4, DM Q15, A1, ad 5). Yet when it comes to self-defense and capital punishment Aquinas’s reasoning seems at odds with itself. One may kill a man in self-defense (ST II-II, Q64, A7). Similarly, just as a diseased limb may be cut off for the sake of the good of the whole, so too may an evildoer who is dangerous to the community be killed for the sake of the good of the whole community (ST II-II, Q64, A2). Herein lies the tension: why does Aquinas hold that it is licit to kill in self-defense or in capital punishment on account of the common good, but that one may never tell a lie on account of the common good? I argue that Aquinas does indeed have a consistent account. Killing and lying are not analogous, despite the prima facie temptation to lump them together.