We simply use resemblance to form an analogous prediction.
The second step of the causal realist interpretation will be to then insist that we can at least suppose in the technical sense a genuine cause, even if the notion is opaque, that is, to insist that mere suppositions are fit for doxastic assent.
According to Guyer, Kant claims that our knowledge of such objective temporal series depends upon our knowledge that they are determined by particular causal laws.
Causality is for Hume, the basis for many of our inferences and deductions about the world. By employing that word, we pretend not to have given the ultimate reason of such a propensity. If it is true that constant conjunction with or without the added component of mental determination represents the totality of the content we can assign to our concept of causation, then we lose any claim to robust metaphysical necessity.
It is easier to follow if one recalls that the universal principle of causality asserts nothing about the nature of empirical phenomena as they are independently of how we experience them. One must sharply distinguish between the general principle of causality of the Second Analogy—the principle that every event b must have a cause a—and particular causal laws: particular instantiations of the claim that all events of type A must always be followed by events of type B.
Though it is highly technical, it touches many issues important to contemporary metaphysics of causation.
This is called an assumption since we have not, as yet, established that we are justified in holding such a principle.