 The relation between ontological and epistemological arguments for idealism is complex. Idealism can be argued for on ontological grounds, and then bring an epistemological argument in its train. Or an epistemological argument can be offered independently of ontological assumptions but lead to idealism, especially in the hope of avoiding skepticism. The first option may have been characteristic of some rationalists, such as Leibniz in his more strictly idealist mood. Both forms of argument are found within early modern British philosophy. We find epistemological considerations pushing toward idealism in both Hobbes and Locke in spite of the avowed materialism of the first and dualism of the second, who therefore obviously did not call themselves idealists. Berkeley argues for idealism on epistemological grounds and then adds ontological considerations in order to avert skepticism, although he calls his position immaterialism rather than idealism. Berkeley’s contemporary Arthur Collier, who explicitly denies the existence of mind-independent matter without giving his own position a name, argues first in an epistemological mood, then moves from epistemology to ontology. Hume, by contrast, although calling himself neither an immaterialist nor an idealist, nevertheless adopts epistemological arguments for idealism similar to some of Berkeley’s, but then uses that position as the basis for a critique of traditional metaphysical pretensions, including those to idealism—while also being drawn to idealism in resistance to what he regards as the natural tendency to dualism. Hume’s critical attitude toward metaphysics is subsequently taken up by Kant, although Kant famously asserts on practical grounds some of the very same metaphysical theses that he argues cannot be asserted on theoretical grounds.