Is it immoral to convince someone of some true proposition P, by exposing them to what you know to be an unsound or invalid argument? For example if I told my friend: "If it rains, the grass will be wet. The grass is wet, therefore, it rained." Now supposing it really did rain, would it be immoral to use this invalid argument to convince her? If we answer in the affirmative, it would seem to lead to some unpleasant conclusions. For instance, it would be immoral to put a sign in my yard that says "Candidate X for City Commission", because the sign might convince people without offering them a sound argument. But we answer negatively, it would seem to justify deception. Using unsound arguments to convince people would give them at best an unjustified true belief, not knowledge. Is there a middle ground here?

Comments

To begin with, I don't accept your example of the political sign. Putting an endorsing sign up in your yard is not an invalid argument--it is simply an expression of your opinion. If someone else is persuaded to vote for a candidate just because you have expressed your opinion in favor of that candidate, then so be it. It won't be the result of a bad or invalid argument--though perhaps their reasoning might be faulted as unsound:

If S is going to vote for C, then I should vote for C.
S is going to vote for C (I can tell from the sign in S's yard).
Hence, I should vote for C.

This isn't invalid, but at least the first premise (and perhaps the second, too, should be rejected.)

On your main question, however, I do think there is somthing wrong with using invalid arguments (at least ones that we know are invalid) to persuade people, both because it might habituate them into bad reasoning habits more generally, and because it is a kind of seduction. Consider: suppose you really believe that another person's best interests would be served by having sex with you (something you want with them). But you think you might not convince him/her just by being honest about your interest. So instead you seduce him/her in ways that are dishonest. Even if the other person's interests are ultimately served as a result of the seduction, the very fact of the seduction seems to me to be a clear violation of at least one interest they have--namely, not to be tricked, cheated, manipulated, or lied to. Using bad arguments that you know are bad is pure manipulation--like lying to another person. Bad medicine, even if it cures something!

Your question raises some fascinating issues. I think it will help to separate your question into two distinct concerns: (1) Is it immoral to use faulty reasoning to convince someone to believe something? (2) Is it immoral to place people in a situation where they might believe something on the basis of faulty reasoning?

My first instinct is that situations involving (1) are likely to be immoral, whereas those involved in (2) are probably not. In cases of the first sort such as cases where you use poor reasoning to convince someone of something, as Professor Smith notes, there is a degree of deception at work. While most moral philosophers don’t think that deception is always a bad thing, they nonetheless think it is bad absent special justification. We can imagine cases where deception is harmless (as in your example, of using faulty reasoning to get someone to believe it rained, when in fact it did rain), or even beneficial (as could happen when you deceive someone to do something that is good for them – like getting them to go to the doctor, or something). But as a general rule, I think we do have a duty not to deceive people, and using faulty reasoning is a mode of deception.

However, I don’t think that holding that it is immoral to use faulty reasoning to convince someone to believe something commits one to saying it is immoral to place people in a situation where they might themselves engage in faulty reasoning. As a parent, I think I should avoid placing my children in such situations because I have a duty to help them learn and develop strong reasoning skills. But I don’t think this is a duty that exists absent particular relationships. Since in these cases you are not actively deceiving anyone, I don’t think you are necessarily doing anything wrong. We can imagine situations where you probably shouldn’t place people in situations where they might engage in faulty reasoning processes, but my sense is that what will make these situations wrong is something other than “that you have put them in a situation where they might engage in faulty reasoning processes”.

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