In these three chapters Augustine deals with the questions of error, lying, and certainty, especially with respect to matters of faith. In particular, Augustine here seems concerned with what later philosophers have dubbed the “ethics of belief.” In other words, he’s focusing more on what our moral duties are with respect to belief rather than how we actually form true beliefs, which is the traditional concern of epistemology.

Error, Augustine writes, is clearly undesirable, but it’s also at times unavoidable, for “it is impossible not to be ignorant of many things.” However, some error is morally culpable. “If someone thinks he knows what he does not know, if he approves as true what is actually false, this then is error, in the proper sense of the term.” This seems to imply that there can be a moral dimension to error, perhaps because we are careless in forming our beliefs, or engage in wishful thinking, etc.

While there may be cases where being mistaken or in error about something may actually benefit us (e.g. we may feel happier not knowing the truth about something, or we may be mistakenly led into fortuitous circumstances), considered in itself error is bad because it goes against the nature of our minds. “To err means nothing more than to judge as true what is in fact false, and as false what is true. It means to be certain about the uncertain, uncertain about the certain, whether it be certainly true or certainly false. This sort of error in the mind is deforming and improper, since the fitting and proper thing would be to be able to say, in speech or judgment: ‘Yes, yes. No, no.’”

However, worse than to be deceived, either innocently or by our own carelessness or epistemic failure, is to intend to deceive someone else. Augustine takes an uncompromising view of lying. If being in error deforms the soul by diverting it from its proper end of grasping truth, lying intentionally misuses language, whose primary function is to act as “a medium through which a man could communicate his thought to others. Wherefore to use language in order to deceive, and not as it was designed to be used, is a sin.”

Augustine concedes that lies may have good consequences as well as that some lies are worse than others, but these circumstances don’t alter the essential nature of the lie. He is clearly taking a deontological view that certain acts are wrong in themselves, regardless of their consequences. Adultery, theft, and lying are wrong even if we can imagine circumstances where we could help someone by engaging in them:

That men have made progress toward the good, when they will not lie save for the sake of human values, is not to be denied. But what is rightly praised in such a forward step, and perhaps even rewarded, is their good will and not their deceit. The deceit may be pardoned, but certainly ought not to be praised, especially among the heirs of the New Covenant to whom it has been said, “Let your speech be yes, yes; no, no: for what is more than this comes from evil.” Yet because of what this evil does, never ceasing to subvert this mortality of ours, even the joint heirs of Christ themselves pray, “Forgive us our debts.”

To understand this it’s illuminating to note that earlier Augustine writes that “the liar thinks he does not deceive himself and that he deceives only those who believe him. Indeed, he does not err in his lying, if he himself knows what the truth is. But he is deceived in this, that he supposes that his lie does no harm to himself, when actually every sin harms the one who commits it more that it does the one who suffers it” [emphasis added].

The suggestion here seems to be that the effect that vice or sin has on the soul of the one who commits them is actually worse than the external effects it may have on others. This harks back to Socrates’ view, in light of being condemned to death by the Athenians, that no evil can truly befall a good man. This is because virtue is the life of the soul and, to borrow a phrase, we should fear that which can kill the soul (i.e. vice) rather than that which can kill the body.

And if truth is also the life of the soul (and, indeed, that Truth from which all truth comes), then it makes sense for Augustine to say that departing from truth actually harms him who lies more than the victims of his deceit. Does this mean, however, that we should be indifferent to the consequences of our actions? Augustine’s account of the wrongness of lying is here couched entirely in terms of its violation of the nature of language (or what it’s for: to communicate thought). Most of us, I suspect, find a blanket prohibition on lying pretty tough to swallow, not just because we may think that “white lies” act as a kind of social lubricant, or get us out of difficult situations, but because we can imagine situations where it is not only permissible, but obligatory to lie, such as the archetypal case of the Nazis at the door seeking Jews hiding in your attic whom they will cart off to the ovens if you don’t lie. In other words, lying in such a case seems not only a forgivable offense, but no offense at all, and in fact not to lie would be the offense in this case.

Whether this is right or not, Augustine certainly has something valuable to say to Christians, “heirs of the New Covenant to whom it has been said, ‘Let your speech be yes, yes; no, no: for what is more than this comes from evil.’” How seriously do most of us take the dominical injunctions to be truthful in our speech?