David Hume defined what is now known as the “Is-Ought” fallacy. Here, I’ll let Mr. Hume speak for himself:
In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it should be observed and explained; and at the same time that a reason should be given; for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it
Basically, you can’t derive an “ought” from an “is”. You can’t say “Bob is homeless, so I ought to give him a roof over his head” without some sort of legwork inbetween the “is” and “ought”.
There is a correlary to this, or a reciprocal version of this oddity that Hume points out that I see a lot in debates about morality, ethics, and the existence of god. I don’t know if I’m the first person to point it out, but lots of people seem to be swayed by it. It is the ought-is fallacy: A person making an argument about how some system of morality ought to be (because if not… uh oh!) and then concludes that this system of morality is.
Recently this has struck me in Adam Lee’s interactions with Peter Hitchens, where Hitchens argues for universal morality, therefore god. Sure, there ought to be a universal, unalterable morality, but just because there ought to be doesn’t mean that there is. The almost universal objection to there not being universal morality is that if there weren’t universal morality, then people could do whatever they wanted.
What if that’s actually how the universe is? Will the rules of the universe automatically change just because we arrive at some observation or conclusion that doesn’t privelage human society? I would think not, but the Ought-Is fallacy assumes otherwise.
This is what those type of arguments look like to me:
P1: There ought to be universal morality
C: Therefore there is universal morality (therefore god)
Another, related instance is where some people contemplate the metaethics of some religion and finds them laudible. Again, maybe that religion has the correct and sensible way of hammering out ethical actions. Maybe it doesn’t. Neither conclusion, however, bears any weight on the truth value of that religion’s other metaphysical claims. Take the following argument:
P1: All cats live in the ocean
P2: Dolphins are cats
C: Dolphins live in the ocean
In this syllogism, the conclusion is true but the argument is horrible. The same sort of error in metaethical reasoning can happen with religions. Maybe some religion has the best and most efficient ethical theory ever encountered. But this fact has no bearing whatsoever on the truth value of any related metaphysics that led to the “true” ethical theory, just like one can’t claim that because the conclusion of an argument is true, it must follow that the premises are true.
While not necessarily a perfect ought-is fallacy, it does follow the same sort of logic. It’s more along the lines of “we ought to do something, therefore whatever led us to do said ‘ought’ is true”. There has to be more legwork between the ought and is, just like in Hume’s original is-ought problem, that builds a solid bridge between the is and ought.