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The Argument From Moral Disagreement, Part 2: Which Argument, Exactly?

Recapping the Moral Argument

In my last article, I presented what's often called "the argument from moral disagreement." According to this argument, there's a lot of disagreement within the subject of morality, and the correct conclusion to draw from this disagreement is that morality is subjective. That is, given both the number of moral issues on which people disagree and depth of their disagreement on many of these issues, we ought to regard moral judgments as more analogous to fashion and culinary judgments than scientific and mathematical judgments.¹

Obviously, whether or not the argument from moral disagreement is correct isn't a trivial issue. For if it is correct, it's difficult to resist the conclusion that "prejudice is wrong," "it's right to show kindness to the poor" and [insert your favorite moral judgment] are, at root, more like "mullets are awesome" than (say) "Denver is the capitol of Colorado." And downstream from this conclusion, it's hard to say how "the Holocaust was really cool" could deserve the response we badly want to give it: "Absolutely not, no matter how sick our tastes may be."

As I stated in my last article, I'm a bit skeptical of the argument from moral disagreement. And in this series I'm going to say why. But first, let's pay a visit to some old friends.

So How's the Argument Supposed to Go?

As a rule of thumb (and I'm talking to you, Coffee Shop debaters), anytime you criticize an argument, the first thing you ought to do is identify the kind of argument you're dealing with. This entails identifying its premises and conclusion, and figuring out how its premises support (or are supposed to support) its conclusion.

What kind of argument is the argument from moral disagreement, then? What are its premises, what is its conclusion, and how do its premises support its conclusion?

The Possibility of a Strong Deductive Argument

According to the argument from moral disagreement, there's a lot of disagreement within the subject of morality, and the correct conclusion to draw from this disagreement is that morality is subjective. OK, so the conclusion of the argument is that morality is subjective. And it looks as if the argument only has one premise — namely, that there's a lot of disagreement within the subject of morality. But if this is right, the argument from moral disagreement amounts to no more than the following:

P-1: There is a lot of disagreement within the subject of morality.

Therefore,

C: Morality is subjective.

But this presentation isn't at all satisfactory — first, because it leaves the force of moral disagreement at the level of our intuitions (which, by the way, are often mistaken) and, second, because it leaves the logical connection between P-1 and C entirely implicit. What can we add to P-1 and C, then, so that it's clear how the argument is supposed to work? Well, how about the following?

P-1: There is a lot of disagreement within the subject of morality.
P-2: For every subject S, if there is a lot of disagreement within S, then S is subjective.

Therefore,

C: Morality is subjective.

Having added P-2, we have an argument that's both explicit and obviously valid. But is this how we should understand the argument from moral disagreement? Not unless we want to be accused of attacking a straw man, for P-2 is obviously false.² For example, there's a lot of disagreement not only over whether or not Shakespeare actually wrote the poems and plays attributed to him, but whether or not anyone named "Shakespeare" even existed.³ But the historical existence of Shakespeare and the truth about whether or not he authored any poems or plays are clearly not subjective matters.

So we need something other than P-2. How about the following presentation of the argument from moral disagreement, then?

P-1: There is a lot of disagreement within the subject of morality.
P-3: For every subject S, if there is a lot of disagreement within S, then S is probably subjective.

Therefore,

C: Morality is subjective.

P-3 is clearly an improvement over P-2, since it can't be falsified by a single example. But we still don't have a good argument here. First, even though P-3 is stronger than P-2, this argument isn't valid, since P-1 and P-3 don't entail C. Instead, they entail the conclusion that morality is probably subjective.

Suppose we add "probably" to C, then? Do we have a good argument now? Well, this addition would give us a valid argument, but we would still lack sufficient reason for thinking that P-3 is true. After all, if we sat down and made a list, we could come up with hundreds (maybe thousands) of examples of objective subjects within which there is a lot of disagreement.⁴ But if we can think of hundreds or thousands of examples of objective subjects within which there is a lot of disagreement, why should we think that, if there is a lot of disagreement within some subject, then that subject is probably subjective?

How else might we get from P-1 to C, then? So far, we've only considered the possibility of deducing C from P-1. But maybe the argument from moral disagreement shouldn't be understood as deductive.

Inductive and Abductive Varieties

If we ditch the idea that the argument from moral disagreement should be understood as deductive in nature, we have two possible ways to interpret it: as an inductive argument and as an abductive argument. To see the difference, consider the following examples (which I've modified from an earlier Nerds' Corner article):

Inductive Argument
Micah has written for TrueU, and he wears tube socks; Denise has written for TrueU, and she wears tube socks; Blake has written for TrueU, and he wears tube socks; therefore, everyone who's written for TrueU wears tube socks.

Abductive
If Michael Moore writes for TrueU, then he wears tube socks; Michael Moore does wear tube socks; therefore, Michael Moore must write for TrueU.

As we can see looking at the first example above, one reasons inductively when one reasons from parts to wholes, or from particular cases to general rules.

But what's going on in the example of abductive reasoning? What's crucial to note there is that, while abductive reasoning bears obvious formal similarities to deductive reasoning, one engages in abductive reasoning for wholly different reasons. While deductive reasoning aims at identifying the logical consequence(s) of some fact, abductive reasoning aims at identifying the best explanation for that fact. In the example above, Michael Moore's writing for TrueU is (facetiously) taken to be the best explanation for his tube-socks-wearing.

Looking at these examples, it should be obvious that the argument from moral disagreement shouldn't be construed as an inductive argument. For while C is relevantly analogous to the conclusion that everyone who's written for TrueU wears tube socks, P-1 bears no relevant analogy to the rest of the inductive example. So it looks like abduction is the only option left.

Formulated abductively, then, the argument from moral disagreement would go roughly as follows:

P-4: If morality were subjective, then there would be a lot of disagreement within the subject of morality.
P-1: There is a lot of disagreement within the subject of morality.

Therefore,

C: Morality must be subjective.

Or, at little more conservatively,

P-4.1: If morality were subjective, then there would probably be a lot of disagreement within the subject of morality.
P-1: There is a lot of disagreement within the subject of morality.

Therefore,

C: Morality is probably subjective.

C O F F E E  S H O P

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Do you think morality is subjective or objective?

Join the discussion!

Taken deductively, these are terrible arguments, for they're both guilty of the logical fallacy "affirming the consequent."⁵ But as we just said, rather than taking them deductively, we're taking them abductively. And as abductive arguments, C should be understood not as a logical consequence of P-1, but as the best explanation for P-1.

So we're finally in a good position to give the argument from moral disagreement a fair and careful analysis. And this is exactly what we'll do in my next article.

Notes

1. For a well-known articulation of this argument, see J. L. Mackie's Ethics: Inventing Right and Wrong (Harmondsworth: Penguin Books, 1977). Back^
2. One "attacks a straw man" when one sets up a weak or indefensible argument and attributes it to one's opponent. Back^
3. See, for example, John Michell's Who Wrote Shakespeare? (New York: Thames and Hudson, 1996). Back^
4. Off the top of my head, there's a lot of debate over whether or not God exists, whether or not humans share a family tree with chimpanzees, whether or not unborn fetuses are human persons, whether or not Truman dropped the A-bomb to intimidate the Soviets, whether or not Goldbach's Conjecture is correct, and so on. But none of these issues is subjective, since none of them has an answer that depends on our personal opinions. Back^
5. Here's a nifty mini-article on Affirming the Consequent:

   Consider the following argument forms:

   Modus Ponens
   If P, then Q.
   P.
   Therefore, Q. Modus Tollens
   If P, then Q.
   Not Q.
   Therefore, not P.

   An argument is valid if the truth of its premises guarantees the truth of its conclusion. Modus ponens and modus tollens are both valid. This is obvious upon considering examples such as the following:

   If Shaq is on a horse, then Shaq is on a mammal; Shaq is on a horse; therefore, Shaq is on a mammal.
   If Shaq is on a horse, then Shaq is on a mammal; Shaq isn't on mammal; therefore, Shaq isn't on a horse.

   But now consider the following argument form, which is universally recognized as logically fallacious, yet bears obvious formal similarities to modus ponens and modus tollens:

   Affirming the Consequent:
   If P, then Q.
   Q.
   Therefore, P.

   At first blush, this argument may appear to be valid, but within the context of concrete examples, it's clearly not. Consider:

   If Shaq is on a horse, then Shaq is on a mammal; Shaq is on a mammal; therefore, Shaq is on a horse.

   If all we know is that Shaq's on a mammal, we can't rationally conclude that he's on a horse. For all we know, he might be on a camel, or a mouse, or a San Antonio Spur. The truth of the statement that Shaq is on a mammal does not, then, guarantee the truth of the statement that he's on a horse.

   Back^