What an "Ad Hominem" Argument Is and Isn't

MOVING TO FRONT FROM AUGUST 25, 2011 (NO PARTICULAR REASON, EXCEPT CONFUSIONS ABOUT 'AD HOMINEM' STILL ABOUND IN CYERSPACE, AND THIS POST WAS POPULAR AT THE TIME)

We take a break from our regularly scheduled programming for a brief detour into a subject that is occasionally addressed in the philosophy blogosphere, and is standard fare in "informal logic" or "critical reasoning" classes:  namely, the ad hominem argument, what it is, and why it is fallacious with repect to the truth of what someone says, but not necessarily with respect to whether they are reliable or whether one is justified in believing them.  There was not a single fallacious ad hominem in my post last week, and while the fact that the random know-nothings that populate cyberspace didn't understand that, it was slightly more surprising that one or two law professors made the same mistake.  So perhaps this can be an educational moment.  (Those who already know what an actual ad hominem fallacy is can move on!)

"Paul Campos is scamming his school and his students" is an insulting statement, but it is not a fallacious ad hominem.  Insults are not fallacious:  they may be warranted or not, fair or not, but they do not, per se, involve the ad hominem fallacy.  In its pure form, the ad hominem fallacy is the fallacy of arguing from a fact about the speaker to the falsity of what the speaker says.  Consider:

Smith claims that heat will flow spontaneously from a cold object to a hot object.

But Smith is a notorious philanderer and drunk.

Therefore, it is false that heat will flow spontaneously from a cold object to a hot object.

In fact, what Smith said is false (he is denying one aspect of the Second Law of Thermodynamics), but the fact that he has bad personal traits does not show it to be false:  the bad personal traits in question are irrelevant to the truth or falsity of whether or not heat will flow spontaneously from a cold object to a hot object.

In this case, the bad personal traits in question (sexual infidelity and alcohol abuse) are also irrelevant to whether Smith is a reliable source of information about thermodynamics:  one can be knowledgeable about basic physics, and be a cheat and a drunk as well.   Contrast that, however, with the following non-fallacious argument:

Smith claims that heat will not flow spontaneously from a cold object to a hot object.

But Smith says he knows this because it came to him in a dream.

Therefore, one is not justified in believing that heat will not flow spontaneously from a cold object to a hot object based on Smith's assertion.

In this example, what Smith said is, as it happens, true (it is now a correct statement of one aspect of the Second Law of Thermodynamics), but a personal fact about the speaker--namely, that the proposition came to the speaker in a dream--is a reason for not believing him, for not treating him as a reliable source of information about thermodynamics.  Why?  Because dreams are not reliable sources of knowledge about the laws of nature.  So here we argue from a fact about the speaker--namely, that his putative knowledge came to him in a dream--not to the falsity of what he says, but to his reliability, to whether we are justified in believing him.

One final case to consider, which involves appeal to a fact about the speaker, but is also not fallacious:

Smith tells his classmate (falsely) that heat will flow spontaneously from a cold object to a hot object.

Smith is a malicious person, who will do anything to get an advantage over his classmates. 

Here a fact about the speaker--his malice and willingness to "do anything" for personal advantage--is offered to explain his false statement, but it also arguably implicates his epistemic reliability as well:  someone motivated mainly by malice and personal gain is probably not a reliable source of information about any subject that implicates his personal advantage and/or might satisfy his malice.  But notice that this last argument presupposes the falsity of the statement in question (it is obviously false, to anyone knowledge about thermodynamics) rather than purporting to establish the falsity:  it only explains the making of the false statement.

Back, now, to Campos the Scammer.

Campos initially made a variety of obviously false generalizations about law professors (e.g., that they are scamming their students, that they are lazy, that they don't really invest much time in class preparation, that they do not produce useful or intellectually serious scholarship, and so on--after being called out, he back-pedalled and began adding qualifiers, but it is the initial false generalizations to which I was responding).  That Campos himself is scamming his students, is lazy, doesn't invest much time in teaching, does not produce scholarship any longer--let alone useful or even good scholarship--is relevant to explaining his propensity to libel his colleagues who do their jobs.  (So, too, his history of making outrageous claims to attract media attention is relevant to explaining this libel, and also bears on his general epistemic reliability as a source of information about law professors.)  This was the point made pithily by my colleague from Maryland, who summed up Campos the Scammer by saying, "A thief thinks everyone steals."  This does not establish that it is false that everyone steals; but if it is false that everyone steals, it explains why someone, namely the thief, would nonetheless claim it is true.  It also bears on the epistemic reliability of the "thief":  since the thief projects his failings on to others, he is not a reliable source of information about the behavior of others insofar as they deviate from his norm.  This appeals to facts about the speaker, but is not a fallacious ad hominem.

Notice, of course, that Campos the Scammer recognizes the importance of facts about the speaker to questions of epistemic reliability; even when anonymous, he emphasized these facts about himself in his first post:

I am a law professor.  I have been one for many years, and hope to remain one for many more.  I have had, by the conventional terms in which such things are measured, a successful career in legal academia.  I am on the faculty of a tier one law school, and have taught at several others.

This was meant to establish his epistemic reliability, his trustworthiness, as it were, as a source about the "dirty little secrets" (as he put it) of the legal academy.  This was not a fallacious argument on his part:  if it were true that he really were a "successful" legal academic, that would be relevant to whether he should be believed.  The difficulty with this argument, as I pointed out, is that one of its premises is false.  But in pointing that out, I am not guilty of a fallacious ad hominem either.

Curiously, Campos the Scammer largely (not entirely) offered fallacious ad hominem arguments in response to me.  The fact, for example, that I have a blog about law schools and produce law school rankings along various dimensions is not relevant to whether or not it is true that Campos is a failed academic, or even to whether or not I am a reliable source of information about whether Campos is a failed academic.  On the other hand, when Campos the Scammer writes sarcastically,

Nor can anyone blame Professor Leiter for refusing to bring his expertise and experience to bear on such matters as the extent to which law schools actually train students to engage in some aspect of the practice of law, given that he has never held any professional position for which a law degree (let alone bar admission) is a requirement. 

he has not made a fallacious argument, since it would be relevant to my reliability as an expert on "the extent to which law schools actually train students to engage in some aspect of the practicde of law" if it were true that I had "never held any professional position for which a law degree (let alone bar admission) is a requirement."  The problem with this argument is that the premise--that I have not practiced law and not been admitted to the bar--is false.  (Why did Campos the Scammer make this false statement about me?  Malice, perhaps, or just laziness.)  Of course, it's also an irrelevant argument, since I didn't claim the expertise in question, but that is a separate issue.

Now take a different case.  A colleague in Chicago wrote to me:

In one post, you asked a good question: “My teaching evaluations, by the way, are a matter of public record, will ScamProf Campos share his?”  Fortunately, Colorado teaching evaluations are publicly available online: https://fcq.colorado.edu/UCBdata.htm.  A review of the evaluations from all twenty-one 1L courses last year shows that Colorado Law students give most faculty quite high ratings but regard Campos as one of the least effective professors -- tied for second-last on the “instructor effective” question, and not because he was a hard professor: students estimate doing a below-average amount of work for his class.  Particularly relevant to Campos’s claimed role as the law students’ champion, his own 1Ls rated him one of the lowest on treating students with “respect” (tied for second-last) and one of the lowest on “availability” to students (second-last). 

I have not verified the claims made about Campos's evaluations relative to his colleagues (but anyone interested may do so), so for the sake of argument, assume the characterization is correct.  Is this a fallacious ad hominem?   The argument here is a bit opaque, so it may depend on what we take my correspondent to be saying, but here is one possibility.

Campos the Scammer claims to be motivated by concern for students (rather than, say, attracting attention to himself, compensating for his own failings, or maliciously libelling his colleagues).

His teaching evaluations suggest he does not have great concern for his students.

That would not be a fallacious ad hominem:  the teaching evaluations are relevant evidence with respect to the motive Campos has claimed, and that motive is relevant to his epistemic reliability (which is why, of course, he has claimed it). 

On the other hand, pointing to the fact (if it is a fact) that Campos is not a very effective instructor and does not show much respect for his students (relative to his colleagues) would be a fallacious ad hominem if offered to show that his claims about the rise in law school tuition were false or that he were not a reliable source of information on that subject.

And that concludes our brief foray into the ad hominem fallacy.

UPDATE:  Mike Livingston (Rutgers-Camden) writes with another fun example:

1.  Brian Leiter says he will not write about Paul Campos again.

2.  Brian Leiter writes about Paul Campos again.

3.  Therefore, Brian Leiter cannot be relied on to make accurate statements--or at least, like Oscar Wilde, is unable to resist temptation.

Premise 2 is arguably false:  I wrote about the ad hominem fallacy, using Campos only for an example!  But let's grant that premise #2 is true, then the argument is not fallacious, though it's not very persuasive:  one example of this kind seems inadequate to support the general claim about reliability in #3.