In his acerbically witty “Idealism: A Victorian Horror-Story (Part II),” David Stove excoriated a certain style of philosophical argument that he called “the Gem” (Stove 1991). He found an ardent supporter in Alan Musgrave, whose “Conceptual Idealism and Stove’s Gem” corrals a range of other idealisms that supposedly thrive on the Gem (Musgrave 1999). To get a fl avor of this style of argument, consider Berkeley’s objection to materialism. Berkeley thought that we cannot even think or conceive of objects that exist “without the mind.” The reason? When we try to think of such objects, we fi nd that “they are apprehended by [the mind],” so that we are not, after all, conceiving of objects as existing without the mind (Berkeley 1710, paragraph 23). As Stove puts it, “you cannot have trees-withoutthe-mind in mind,” for “you cannot have trees-without-the-mind in mind, without having them in mind” (1991, 139-140). At best, you can have trees-in-the-mind in mind. And that, thinks Berkeley, is precisely what we do have in mind. Trees-without-the-mind are not even conceivable. What remains is Berkeley’s immaterialist universe.