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Where does the idea of cause come from?

We never see more than one thing following another, never the necessary link: where, then, does the idea of cause come from, which experience never shows?

Objects to Empiricism

Hume, Kant · A Treatise of Human Nature, I.iii.14

1. Empiricism promises to trace every idea back to a sense impression. Let us test it on the idea of cause: when one ball strikes another, what exactly do we perceive?
2. Two motions in succession, a constant conjunction, but never the force that would produce one by the other, nor the necessary link between them. The eye sees no 'must': necessity is not perceived.
3. Yet we judge that the cause necessarily produces the effect, and that judgment holds for all cases to come. But such universal necessity cannot be read off a collection of particular, past cases: something is added that does not come from the senses.

Therefore So either the idea of necessary connection is an illusion (Hume), or the mind supplies it from its own resources (Kant): in either case, experience alone does not suffice to ground knowledge.