Steelman
Is–ought fallacy
Also called hume’s law, hume’s guillotine, naturalistic fallacy (loosely).
Deriving what ought to be purely from what is.
What it is
Concluding what ought to be done (a moral or evaluative claim) from premises that only describe how things are, with no evaluative premise to bridge the gap.
The pattern
X is the case. Therefore X ought to be the case, or we ought to do Y.
An example
“In nature, the strong outcompete the weak. So society ought to be organized so the weak lose out.”
How nature works doesn’t tell us how we should treat each other. The argument needs a hidden premise that nature’s way is the right way, and that premise is doing all the work.
Why it fails
Facts alone don’t settle values. To reach an “ought” you need a premise about what matters, and that premise is often left unstated. Bringing it into the open lets it be examined.
When it’s not a fallacy
Most lists skip this part. Calling a fair point a fallacy is a mistake too.
It can be fair when
- The “ought” premise is implicit but uncontroversial: “This water is poisoned, so you shouldn’t drink it” relies on the obvious premise that you shouldn’t drink poison.
- Philosophers still debate whether an “ought” can ever follow from an “is”. The practical lesson is to state the evaluative premise openly.
Try one
A question from the app. The wrong answers are its usual look-alikes.
Town hall on the minimum wage. Greg, who runs a diner: “Cooks in this town make about $11 an hour, and I fill every shift.” Tasha: “That doesn’t mean $11 covers rent.” Greg: “It means $11 is what that work is worth here. That’s the fair wage, and the city shouldn’t touch it.”
What’s the flaw?
Greg goes from what cooks are paid and accept (a fact) to what they should be paid (a judgment of fairness). That jump needs a value premise, that whatever the market pays is the fair wage, and he never argues for it. It may be true, but it has to be argued; jobs getting filled at $11 only shows what the market pays.
A fair reply
“That’s what the job pays now, but why does that make it the right amount?”
Often confused with
- Appeal to nature
Appeal to nature is the special case where the “is” is “this is natural”.
Where the name comes from
The name is the jump itself: from “is”, how things are, to “ought”, how they should be. “Hume’s law”, after the philosopher David Hume, is the rule that facts alone can’t get you to an ought. “Hume’s guillotine” pictures that rule as a blade slicing facts off from values. “Naturalistic fallacy” strictly means defining “good” as a natural property like “pleasant”, but it’s loosely used for this jump.
David Hume raised the problem in A Treatise of Human Nature (1739–40), noting how writers slide from “is” to “ought” without explanation.
Sources
- Is–ought problem, Wikipedia
- Fallacies, Bradley Dowden, Internet Encyclopedia of Philosophy
In the app
Practice spotting it on arguments that sound real.
Steelman has more examples of is–ought fallacy, how to answer it in a real conversation, and practice rounds that mix it with its look-alikes, so you learn the difference, not just the name. Coming soon to iPhone and Android.
You’re on the list.
We’ll email you the day Steelman is out.
Thanks for offering to test. We’ll write before the beta with how to join.