 He gives a (by now) familiar list of reasons for doubting the certainty of things. First, disagreement among competing theories gives some initial doubt. Second, a few cases of sensory skepticism (e.g., a shadow cast by the sun appearing to remain still, when in fact it is slowly moving as the day passes; the apparently small size of celestial bodies) lead him to lose confidence in all of his sensory beliefs. This distrust of his senses also suggests, third, that another of his faculties—reason itself—may be faulty, and he wonders whether even apparent logical truths might be false. And finally, he concludes by invoking dream skepticism. After setting up these doubts, he says the following: