All true knowledge is ultimately based on "observed evidence," but objectivists do not claim that causality can be deduced from direct observation of evidence. Objectivists believe that causality is based on the law of identity, that a thing is what it is, and that its behavior is determined by its identified nature. The reason a billiard ball struck by another billiard ball moves in the direction it does is because of the nature of billiard balls. Replace a billiard ball with anything else (an egg or ball of yarn) and the behavior will be completely different.
What causes anything to behave as it does is the nature of those things, and the nature of all those things it has any relationship with or to.
I am not refuting what you said, only trying to refine it in terms of what objectivists actually claim.
[You may check this out in the section of Objectivism: The Philosphyof Ayn Rand, entitled: "Causality as a Corollary of Identity".]
Hank
I sure hope not - that sounds suspiciously inductive to me...