A Quick Argument for Objective Morality

Here’s a quick deductive argument for moral objectivism, where by moral truths being “objective” I mean that they hold independently of human opinion. (This is a stipulative definition of moral objectivism; though similar definitions can be found in the philosophical literature, not everyone uses the same definition).

The Argument

1. It is morally wrong for a man to torture an infant just for fun.
2. It would remain morally wrong to torture an infant just for fun even if a baby torturer thought otherwise and killed everyone who didn’t agree with him.
3. If (1) and (2) are true, then objective morality exists.
4. Therefore, objective morality exists.

The above argument is logically valid (i.e., impossible by the rules of logic to have true premises and a false conclusion) so the only way it can fail to be sound is with an untrue premise. The difficulty for those who wish to say the argument is sound is finding an untrue premise once the premises are correctly understood.

Premise (3) is correctly understood as a material conditional, meaning it’s equivalent to “It is not the case that both (1) and (2) are true with <objective morality exists> being false.” So, the only way (3) can be false is if both (1) and (2) are true yet <objective morality exists> is false. Premise (3) being a material conditional like this is good enough for (1)-(4) to be logically valid.

But how to justify that premise (3) is a true material conditional? The justification for premise (3) is that once we accept the truth of (1) and (2) it leads to moral objectivism via this step-by-step reasoning:

1. In the thought experiment of premise (2), something remains morally wrong even when all human opinion thinks otherwise (since the torturer killed off everyone who doesn’t agree with him);
2. in which case the moral truth “It’s morally wrong for a man to torture infants just for fun” would be holding despite human opinion;
3. in which case it seems we have an example of an objective moral truth (i.e., holding true independently of human opinion) thereby giving us objective morality.

If (a), (b), and (c) are all true as they seem to be, then we have an example of an objective moral truth. For those who disagree, do you disagree with (a), (b), or (c)? If so, which one(s)? Remember, the idea is that (a), (b), (c) are correct if (1) and (2) are true. So for those who accept (1) and (2) yet reject moral objectivism, which item—(a), (b), or (c)—is false?

Since premise (3) is a material conditional, premise (3) being false requires that premises (1) and (2) are both true. So instead of disagreeing with premise (3), one could concede that premise (3) is true (i.e., “It is not the case that both (1) and (2) are true with <objective morality exists> being false”) in favor of believing that premise (1) is untrue or that premise (2) is untrue.

You could deny premise (1). Do you believe there’s nothing morally wrong with torturing infants just for fun? (Note that premise (1) doesn’t say whether the moral wrongness is objective; premise (1) is just about whether it is morally wrong at all for a man to torture infants just for fun.)

You could bite the bullet and deny premise (2), say it’s not morally wrong for a man to torture infants just for fun as long as he believes otherwise and kills everyone who doesn’t with him. Do you think that’s a reasonable belief?

Why I Like It

I think this is a good deductive argument for moral objectivism because it quickly reveals how intellectually pricey it is to deny objective morality. It’s not reasonable to believe that there’s nothing morally wrong with torturing infants just for fun, so premise (1) is not plausibly false. Likewise, it’s not reasonable to believe that it’s not morally wrong for a man to torture infants just for fun as long as he believes otherwise and kills everyone who doesn’t agree with him; so premise (2) is not plausibly false.

This forces the disbeliever of moral objectivism in a very intellectually uncomfortable position, especially in a debate, because even if the disbeliever is willing to bite a bullet and reject a premise, most people won’t find the disbeliever’s premise rejection tenable.