Lying and the Nature of Assertion
According to Aquinas an action is assessed morally according to what is essential – rather than accidental – to it. This is an extremely fruitful way of thinking about morality, and can provide resources for overcoming difficult cases, including for Christianity. For example, one might wonder what is wrong with killing an innocent person if we knew they would be brought to heaven: in fact, one might wonder why we don’t have an obligation to kill an innocent person if we thought they would go to heaven.
Aquinas’s theory can tell us why that action would be wrong. It is because what is essential to the action of killing an innocent person (i.e., murder) is destroying their nature; it is only accidental that they get to heaven. Our murdering action does not entail they get to heaven. Hence, their getting to heaven (if they get there) is incidental. This is because it is ultimately God’s action by which somebody gets to heaven, not ours. And because actions must be judged by what is essential to them, we can consistently maintain, in Aquinas's view, that it is always wrong to kill an innocent person. This is not to say all killing is intrinsically wrong (we’ll consider this shortly), even if all killing essentially involves the destruction of some nature.1
Now, an important difference between killing and lying is this. Killing is a natural species of action, not a moral species.2 Killing, in other words, is not immoral by default – we kill things all the time, from plants and animals and (indeed) other humans. Whether killing is immoral depends on what is being killed and why. Lying is not like this. Lying is a moral species that is per se disordered unlike killing. If this distinction can be maintained, then various analogies where killing is occasionally permitted for some greater or common good will break down in trying to argue the same for lying.
We must now ask what is essential to lying before considering “the Nazi at the door” example. Traditionally, what is essential to lying is communicating something contrary to one’s true thoughts. That is what makes a lie a lie, and thus it is certain that whenever a lie is committed one speaks contrary to one’s true thoughts. Now, if it is correct that the power of communication is naturally directed toward the good of expressing our true thoughts, it follows that lying is a perversion of faculty, and always an intrinsic evil (here I assume knowledge of essentialist metaphysics). What is not certain are any outcomes of lying: surely, it is accidental whether the Nazi at the door does or does not leave you, and whoever you are housing, alone. Thus, if Aquinas is right, and actions are to be judged by what is essential rather than accidental, then lying is always intrinsically wrong via the perversion of faculty, regardless of whatever may be the case accidentally.
How wrong is an interesting question (venial sin, mortal sin?), but that it is wrong follows from just a few plausible assumptions that inform Aquinas’s action theory. Not just that an action is to be judged by what is essential to it but also that the power of communication has expression of one’s true thoughts as its proper end (natural good). One might try to push against the latter assumption by suggesting our communication power has alternative uses but Aquinas is more thorough and articulate than many have assumed in this regard.
For Aquinas does not say communication has only the function of assertion, but rather it is undoubtedly true that the nature of ASSERTION (or endorsement, as Alex Pruss puts it) is to express truth. In other words, one can leave open whether our communicative powers in general have alternative functions than assertion (in an obvious sense they do, because not everything meaningful we utter is assertive; some is interrogative); one cannot, however, reasonably maintain that the nature of assertion is other than getting the truth across. If one reads Aquinas carefully, they will see that is where his analysis of lying lies: not in relation to the nature of communication vaguely considered, but in relation to the nature of ASSERTION. And because lying always intentionally speaks contrary to what one believes in the form of assertion, it is always contrary to the nature of assertion, and therefore always evil. Thus lying is a moral species in a way killing is not given the underlying analysis. Which means any appeal to justified killing for some greater good cannot be used to argue lying could be justified for some greater good, because lying, unlike killing, is intrinsically (per se) evil. To assert otherwise (including to intuitions on the matter), is to beg the question.
Of course, we could argue that we could never know (with certainty) that somebody would get to heaven if we killed them, but that is a secondary line of response.
As John Skalko explains, “To begin with, killing in itself is a natural species of action, while lying is a moral species. Natural species are morally neutral, while moral species are not. Killing cannot receive its moral species until it is known what the materia circa quam of the action is. It makes a world of difference whether the killing is of a plant, an animal, an innocent human being, or a guilty one. Killing in an act of just war and due capital punishment is good, but killing the innocent is evil. Only certain species of killing are morally evil, but killing in itself as a natural species is not. Lying, on the other hand, is not a natural species. It is evil in its genus on independent grounds even before broken down into its species. Ergo, killing and lying are not analogous.” Why Did Aquinas Hold That Killing Is Sometimes Just, But Never Lying?