This paper discusses two questions about Hume's philosophy. Question 1: whether Hume's skepticism about causation and induction is radical or moderate? By analyzing the quotations from Hume and reconstructing his arguments, this paper tries to show that Hume does not assert that there is no necessary connection between cause and effect, he just wants to say that we cannot know whether or not there is such kind of connection; similarly, he does not and even cannot prove that objective causation does exist. So, Hume is not a realist about causation, not an extreme skeptic, let alone an agnostic; actually he advocates the self-discipline, prudence and humility of human reason. Question 2: whether Hume's formulation and application of conceivability principle (CP) is problematic or not? Similarly, by analyzing textual evidence and reconstructing Hume's arguments, this paper tries to show that Hume does articulate CP, and applies it to four different cases, of which two are legitimate and effective: to apply it to prove that causal reasoning is not logically necessary, and to apply it to prove that it is not the case that propositions about matters of fact is true or false only based on logic and reason. However, in using CP and conceivability argument to refute the necessity of causation and the uniform law of nature, Hume fails because he does not distinguish different kinds of necessity. The metaphysical version of CP is highly controversial.
