# Idealism_First published Sun Aug 30, 2015; substantive revision Fri Feb 5, 2021_This entry discusses philosophical idealism as a movement chiefly in the eighteenth and nineteenth centuries, although anticipated by certain aspects of seventeenth century philosophy and continuing into the twentieth century. It revises the standard distinction between epistemological idealism, the view that the contents of human knowledge are ineluctably determined by the structure of human thought, and ontological idealism, the view that epistemological idealism delivers truth because reality itself is a form of thought and human thought participates in it, in favor of a distinction earlier suggested by A.C. Ewing, between epistemological and metaphysical arguments for idealism as itself a metaphysical position. After discussing precursors, the entry focuses on the eighteenth-century versions of idealism due to Berkeley, Hume, and Kant, the nineteenth-century movements of German idealism and subsequently British and American idealism, and then concludes with an examination of the attack upon idealism by Moore and Russell and the late defense of idealism by Brand Blanshard. With the possible exception of the introduction (Section 1), each of the sections below can be read independently and readers are welcome to focus on the section(s) of most interest.* * *## 1. IntroductionThe terms “idealism” and “idealist” are by no means used only within philosophy; they are used in many everyday contexts as well. Optimists who believe that, in the long run, good will prevail are often called “idealists”. This is not because such people are thought to be devoted to a philosophical doctrine but because of their outlook on life generally; indeed, they may even be pitied, or perhaps envied, for displaying a naïve worldview and not being philosophically critical at all. Even within philosophy, the terms “idealism” and “idealist” are used in different ways, which often makes their meaning dependent on the context. However, independently of context one can distinguish between a descriptive (or classificatory) use of these terms and a polemical one, although sometimes these different uses occur together. Their descriptive use is best documented by paying attention to the large number of different “idealisms” that appear in philosophical textbooks and encyclopedias, ranging from metaphysical idealism through epistemological and aesthetic to moral or ethical idealism. Within these idealisms one can find further distinctions, such as those between subjective, objective and absolute idealism, and even more obscure characterizations such as speculative idealism and transcendental idealism. It is also remarkable that the term “idealism”, at least within philosophy, is often used in such a way that it gets its meaning through what is taken to be its opposite: as the meaningful use of the term “outside” depends on a contrast with something considered to be inside, so the meaning of the term “idealism” is often fixed by what is taken to be its opposite. Thus, an idealist is someone who is not a realist, not a materialist, not a dogmatist, not an empiricist, and so on. Given the fact that many also want to distinguish between realism, materialism, dogmatism, and empiricism, it is obvious that thinking of the meaning of “idealism” as determined by what it is meant to be opposed to leads to further complexity and gives rise to the impression that underlying such characterizations lies some polemical intent.Within modern philosophy there are sometimes taken to be two fundamental conceptions of idealism: 1. something mental (the mind, spirit, reason, will) is the ultimate foundation of all reality, or even exhaustive of reality, and 2. although the existence of something independent of the mind is conceded, everything that we can _know_ about this mind-independent “reality” is held to be so permeated by the creative, formative, or constructive activities of the mind (of some kind or other) that all claims to knowledge must be considered, in some sense, to be a form of self-knowledge.