Have any philosophers argued that ad hominems are sometimes valid?

Question

As far as I can tell, the position that ad hominem attacks are always invalid seems to be widespread within the philosophical community. I'm not entirely convinced that this is a reasonable position, however. I agree that many ad hominem attacks are invalid, I'm just not convinced that they all are.

For example, if somebody attempts to build a logical argument, with explicit premises and explicit conclusions, then I agree that attempting to dismiss such arguments by attacking the integrity (etc.) of the person making the argument is usually the wrong thing to do. You should deal with their argument, or admit that you haven't yet thought enough about it to give their reasoning the well-conceptualized critique it deserves.

However, most arguments aren't all that clear or logical. In fact, most "arguments" we hear in the media are little more than assertions, with words like "because" sprinkled in for persuasive effect. I think its acceptable to use ad hominems to dismiss such arguments. If, for example, an untrustworthy character says that we should invest more in roads because the benefits of building more roads exceed the costs, I think a useful and valid counterargument is to list times when that person has been intentionally dishonest, in order to cast (valid) doubt on their premise that the costs will exceed the benefits.

As a general rule, I think that filtering messages by the perceived integrity of the speaker is quite useful.

My questions are twofold.

Q0. What are the usual arguments against ad hominems, and how broad is their scope? That is to say, in what situations do they attempt to establish that ad hominems are an invalid form of rebuttal?

Q1. Have any philosophers argued that ad hominems are sometimes valid rebuttals, and if so, under what circumstances are they valid according to said philosophers?

Answer 1

I remember reading about this (Ad Hominem) on Wikipedia in the past and they answer your questions (Q0 and Q1) pretty clearly:

Non-fallacious reasoning

When a statement is challenged by making an ad hominem attack on its author, it is important to draw a distinction between whether the statement in question was an argument or a statement of fact (testimony). In the latter case the issues of the credibility of the person making the statement may be crucial.

So in essence, yes, Ad Hominem is not always invalid just because it's Ad Hominem. If the credibility of the person issuing the statement is of importance to it's conclusion, then Ad Hominem could be entirely valid.

To answer your title question: Have any philosophers argued that ad hominems are sometimes valid? - Yes

Gary N. Curtis, owner of the website: Fallacy Files.org and Philosophy PhD is the source for the Wikipedia quote given above. He states eloquently:

The main thing to keep in mind is the distinction between argumentation and testimony. The whole point of logic is to develop techniques for evaluating the cogency of arguments independently of the arguer's identity. So, ask the question: is the person being criticized arguing or testifying? Are reasons being presented, or must we take the person's word for something? If the person is arguing, the argument should be evaluated on its own merits; if testifying, then credibility is important.

Answer 2

First, it should be remembered that ad hominem is an informal fallacy, and not a formal one. This means that its use has no bearing of the logic of the argument. It's use in formal debate is therefore considered invalid, because it doesn't help anyone evaluate the argument itself.

Your use is a good one, and surely an ad hominem in such a scenario is appropriate. However, again, it has no real bearing on the actual logic of the argument. That means that despite being proper to bring up in some informal debate, it's never valid in the proper sense. If someone who has a history of being truthful in their argumentation brings up the same argument that someone who has a history of being dishonest, the argument is still the same.

The ad hominem here then doesn't affect how we evaluate the argument, but whether we ought to evaluate it, and how much of our time we should invest in evaluating it.

Answer 3

It's important to distinguish between the truth of an argument's premises and the validity of the deduction. A person's integrity has no relevance in evaluating the validity of an argument. A person's integrity does come into play when evaluating the truth of their premises.