he Necessity of Idealism Aaॸॵॴ S५७aॲ aॴ४ Tyॸॵॴ Gॵॲ४ॹ३८ॳ९४ॺ In Idealism: New Essays in Metaphysics, Kenneth L. Pearce and Tyron Goldschmidt (eds.), Oxford University Press, ৼ৺৻. ৻ Introduction We formulate a version of idealism and argue for it. Sections ৼ and ৽ explicate this version of idealism: the world is mental through-and-through. Section ৼ spells this out precisely and contrasts it with rival views. Section ৽ draws a consequence from this formulation of idealism: idealism is necessarily true if true at all. Sec- tions ৾ and ৿ make the case for idealism. Section ৾ is defensive: it draws from the conclusion of Section ৽ to reply to a central, perhaps the central, anti-idealist argu- ment. Section ৿ is on the ofense: it develops a new argument for idealism based on the contemporary debate in philosophy of mind. he contemporary debate in philosophy of mind has been dominated by physicalism and dualism. While ide- alism has been historically inluential, the contemporary debate has neglected it. If the reason is that defenses of idealism have not engaged so much with the rest of philosophy of mind, we hope to rectify that a litle. ৼ Idealism Idealism is the view that the world is in some sense mental. But not just men- tal: thoroughly mental, wholly mental, mental through-and-through. It is incon- sistent with, e.g. the contemporary panpsychist view that while everything, from humans to amoebas to quarks, has thoughts, those things also stand at some dis- tance from one another and move over time and do other things that are not to be understood mentalistically. he panpsychist world isn’t thoroughly mental. On the other hand, Idealism is consistent with there being physical things; indeed, it is consistent with the world being thoroughly physical, wholly physical, physical through-and-through. Or, at least, it’s not trivially inconsistent with those claims. It’s not obviously incoherent to suppose that the world is both thoroughly mental and thoroughly physical. hat would be the case if every mental aspect of the universe were itself physical, and vice versa. To ix ideas, we introduce some terminology. A thing is concrete if and only if it is spatiotemporal. A thing is mental if and only if it has some mental feature, and purely mental if and only if it has only mental features. ৻ Likewise, a thing is physical if and only if it has some physical feature, and purely physical if and only if it has only physical features. Idealism is the view that all concrete things are purely mental. Physicalism is the view that all concrete things are purely physical. Impurism is the view that no ৻ We use feature to cover both (monadic) properties and (polyadic) relations. hus, one can say “John has the feature of being six feet tall” and “Harry and Sally have the feature of being in love”. hus, a thing is mental if and only if it has some mental property or stands in some mental relation, a thing is purely mental if and only if it has only mental properties and stands in only mental relations, and so on.