In my last two posts, I discussed two ways of deceiving others and pointed out that both were acceptable at some time or other. But neither form involved the highest form of deception – claiming something to be true when we believe that it is false. Lying is never morally permissible.
The first reason why lying is wrong is that it is contrary to the natural purpose of speech. Through speech, we may express our true opinion, command, wish or desire. This is what speech does by nature. But if we declare that something is our true opinion when it is really not our true opinion, then we are acting contrary to the nature of speech itself. The natural purpose of something is the same as what is good for something. So acting contrary to that natural purpose is immoral. Therefore, lying is immoral.
The second reason why lying is wrong is that it is contrary to any moral motivation for deception. Since something that is contrary to moral motivation is wrong, lying is wrong. Deception is morally permissible – even in the message – when murder to attempted. But it is permissible because its success is tied to the immorality of the act of murder. The act of deception would fail if it were attempt against a wise person. But lying would not necessarily fail against a wise person. If a wise person has no good reason to believe that he is being lied to then he will believe a simple lie. Since the motivation is to prevent murder, the means are too broad.