Ad Hominem ｜ Liffel（リッフェル）

This entry explains the ad hominem fallacy, informally known as a personal attack. It is one of the most frequently observed fallacies.

Let’s begin.

What Is Ad Hominem?

Ad hominem is making the person behind an argument — their character — the target of debate, rather than the argument itself.

Let’s look at an example.

It’s drizzling. Should I use an umbrella?

You should. Getting wet puts you at risk of catching a cold.

You’re always catching colds yourself. I don’t think I should listen to you, so I won’t use an umbrella.

What Bear is doing here is ad hominem. Let’s analyze the exchange.

The question is “Should I use an umbrella?” Each animal’s argument breaks down as follows.

Speaker	Claim	Premises
Panda	Use one.	Because getting wet puts you at risk of catching a cold.
Bear	Do not use one.	Because Panda, who claims that getting wet puts you at risk of catching a cold, is always catching colds himself (and therefore cannot be trusted).

As you can see, Bear’s premise is that “Panda cannot be trusted.” This is not about the question “Should I use an umbrella?” — it is about Panda’s character. This kind of move, and this kind of argument, is what we call ad hominem.

Keyword

Ad hominem: making the person behind an argument — their character — the target of debate, rather than the argument itself (and also the kind of argument that does this).

Character

By “character” here, we essentially mean what this site calls a person’s brand. Take a look at the following slide.

As shown, a person’s “character” is made up of their attributes, appearance, and bearing, together with what they have done for you in the past (their track record). The finer-grained elements are summarized in the table below.

This entry focuses on why basing an argument on these things is wrong, so we will not unpack the images here. Readers who want a deeper treatment should consult the following entry.

[Not Translated] 説得の構造

Why Ad Hominem Is Wrong

Why, then, is ad hominem wrong?

This is not intuitive. When we examine the merits of an argument, no one is completely indifferent to the character of the person making it. Everyone naturally cares, before getting to the argument itself, about things like whether they know the speaker and whether the speaker can be trusted.

However, character has no bearing on the question. Since anything irrelevant cannot count as a legitimate premise, any argument that uses character as a premise is wrong, that is, irrational¹. Put simply, it misses the point.

We can put it another way. If incorporating character into our premises were legitimate, such a premise would be all-powerful. For instance, if there were a person with top-tier character (say, a Nobel laureate with celebrity-level looks), everything that person said would have to be counted as right. Conversely, nothing said by someone with the lowest-tier character could be accepted.

That amounts to treating the person as an oracle (or, in the opposite case, as someone whose words must always be rejected). Treating an oracle’s words as right is faith, not thinking. If we want to think, we have to separate character from the argument.

Point

Character has no bearing on the question or the argument.

Names for the Act of Targeting Character

The act of making character the target of debate goes by many names besides “ad hominem.” The slide below organizes them.

Ad hominem and related terms

The horizontal axis classifies whether the act takes place inside a debate or outside it; the vertical axis classifies whether character is used as a premise to affirm or to negate the opposing argument.

For the content itself, please refer to the slide. Here, we will cover the points that require special attention.

Using Character to Affirm an Argument Is Also Wrong

To begin with, ad hominem in the strict sense also applies when character is used as a premise to affirm an argument, and that too is wrong. Let’s look at an example.

It’s drizzling. Should I use an umbrella?

You should. Getting wet puts you at risk of catching a cold.

You’re a doctor, so I’ll take your word for it. I’ll use an umbrella.

In this case, the bear is affirming the argument on the premise that “the panda is a doctor.”

Affirmation and negation are reversed from the earlier example, but in terms of “using character as a premise, which makes the reasoning wrong,” the two cases are the same.

Authoritarianism

That said, in Japan, the term “ad hominem” is in most cases used to mean “using character as a premise to negate an argument.” The reasons are as follows.

First, what makes us want to commit ad hominem in the first place (though we should not) is a clash of arguments. When we agree with the other side’s argument, we just look at its content and say “I think so too.” It is when we want, somehow, to negate the other side’s argument that we start picking at their character.

Also, “using character (especially attributes) as a premise to affirm an argument” has another name: “authoritarianism” (or “appeal to authority”).

And reasoning by authoritarianism is normal in Japan (it is regarded as right). Because it is not perceived as wrong, it is rarely pointed out as “that is ad hominem / authoritarianism.”

This topic gets long if we dig into it, so we will leave it here. In any case, authoritarianism is a form of ad hominem, and it is wrong. Do not get this point wrong.

Readers who want to study this in more depth should consult the following book.

The Causes and Countermeasures of Ad Hominem

Finally, let’s think about the causes of ad hominem and what to do about it. We will start with the causes.

Causes

To begin with, the cause of committing ad hominem comes down to not recognizing that ad hominem is wrong.

As noted above, in Japan, reasoning by authoritarianism is, far from being regarded as wrong, treated as the “standard way of thinking.” Put differently, since tying arguments to character is not seen as a problem in Japan, ad hominem occurs as a matter of course.

In other words, the root cause of this situation is not knowing what should be regarded as a “right” way of thinking. In school, we are taught correct answers, not the right way of thinking. That is where the fundamental problem lies.

Countermeasures

The countermeasure is to recognize that ad hominem is wrong and then learn the right way of thinking.

The fact that ad hominem is wrong has already been explained. For the right way of thinking, please refer to the following category.

[Not Translated] ロジカルシンキングのすべて

This concludes our discussion of ad hominem. Next, let’s consider the problem of making “the manner of delivery” the target of debate. This too is a kind of irrelevance. Please continue to the following entry.