What is the passage mainly arguing?

An argument that moves from facts to duties hides a value that should be named. (The passage describes the silent jump from is to ought and ends by asking for the missing premise to be named.)

What was Hume's complaint?

That a new kind of word entered the argument without being introduced. (The first paragraph says this directly, and adds that his complaint was not that the conclusion was wrong.)

According to the passage, why do arguments about what is natural often go wrong?

The value step, that natural things are good for us, is added without defense. (The example says nothing follows from natural until a value is added, and that this added step is where disagreement hides.)

In this passage, a prescription is

a statement about what should be done. (It is set against description: a description says how things stand, a prescription says what to do.)

From Is To Ought: Level 4 Reading Comprehension Questions

Reading the moral writers of his time, David Hume noticed a quiet move that almost nobody defended. An author would begin with ordinary claims about how the world is: people live in groups, promises make trade possible, cruelty causes pain. Then, without warning, the sentences would change shape. Instead of saying what is the case, they would say what ought to be done. Hume's complaint was not that the conclusion was wrong. It was that a new kind of word had entered the argument without being introduced.

The gap matters because facts and values answer different questions. A description tells you how things stand; a prescription tells you what to do about it. From the fact that a food is natural, nothing at all follows about whether you should eat it, until someone adds a value: that natural things are good for us. That added step is where the real disagreement usually hides, and it is the step most arguments skip.

This is why careful thinkers ask for the missing premise. Naming it does not settle the dispute. It moves the argument to the place where the dispute actually lives.

Comprehension questions