 So Henry’s arguments, far from showing that certainty is possible through divine illumination, actually lead to a pervasive skepticism. Scotus counters that we can show that skepticism is false. We can in fact attain certainty, and we can do so by the unaided exercise of our natural intellectual powers. There are four types of knowledge in which infallible certainty is possible. First, knowledge of first principles is certain because the intellect has only to form such judgments to see that they are true. (And since the validity of proper syllogistic inference can be known in just this way, it follows that anything that is seen to be properly derived from first principles by syllogistic inference is also known with certainty.) Second, we have certainty with respect to quite a lot of causal judgments derived from experience. Third, Scotus says that many of our own acts are as certain as first principles. It is no objection to point out that our acts are contingent, since some contingent propositions must be known immediately (that is, without needing to be derived from some other proposition). For otherwise, either some contingent proposition would follow from a necessary proposition (which is impossible), or there would be an infinite regress in contingent propositions (in which case no contingent proposition would ever be known). Fourth, certain propositions about present sense experience are also known with certainty if they are properly vetted by the intellect in light of the causal judgments derived from experience.