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The is–ought gap — Philosophy, 14–17 years

Why facts alone do not automatically tell us what we ought to do. Philosophy, 14–17 years.

Facts need a value bridge

A fact describes how things are: the lake is polluted, or the train is late. An ought says what should be done: clean the lake, or wait for the train. Facts matter, but a further value or goal is needed to move from description to obligation.

Stopping a hidden step

People often present moral conclusions as if facts had already decided them. In the 18th century, David Hume noticed that writers moved from “is” statements to “ought” statements without explaining the change. Naming the gap helps us uncover the value assumption in an argument.

Finding the missing premise

Argument: “This jacket is expensive, so you should not buy it.” First, the fact is that it costs 200 euros. Second, the conclusion says not to buy it. What is missing? A value premise such as “You should avoid purchases that cost more than you can reasonably afford.” Only then does the conclusion follow.

Facts do not carry their own orders

The usual mistake is to treat “natural” as automatically meaning “good”, or “common” as meaning “right”. This feels reasonable because we learn from nature and from what most people do. But description and approval are different; an extra principle is needed to connect them.

Clearer public decisions

This distinction improves debates about school rules, public health, technology, and the environment. When someone says what we must do, ask which facts support the claim and which value makes it a duty. You can then disagree about the value openly instead of arguing as if it were a mere fact.

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