8. A passage from Kripke

Here’s a quick argument from Saul Kripke’s Naming and Necessity (Harvard 1980):

If something is known a priori it must be necessary, because it was known without looking at the world. If it depended on some contingent feature of the actual world, how could you know it without looking?

Kripke doesn’t actually endorse this argument. He thinks it is wrong. Even so, the passage does capture a natural way of thinking and Kripke relays it very succinctly.

The question is whether a truth known a priori is bound to be a necessary truth and the passage says yes. Kripke himself disagrees and thinks that some a priori truths are only contingently true, but never mind this.

Our question just concerns the structure of the argument shown above. What is it?