MONISM, in philosophy, generally denotes any ontological theory according to which all that exists is in some sense one (Gr. yovos, one). The term monism was first introduced by the Ger man philosopher C. Wolff (1679-1754), but came into vogue chiefly through the influence of Haeckel and Ostwald, the leaders of the "Society of Monists" (Monistenbund) founded in 1906. Wolff used the term monism simply in contrast to dualism, and he recognized only two kinds of monism, namely, materialism and idealism. Since then, however, the term has received many other applications, and the present varieties of monism are legion. It is not proposed to do more here than to indicate briefly the most im portant of them. To avoid unnecessary complication and confusion it is perhaps best to follow the more usual tendency and to restrict the term monism to what is sometimes called "substantival" monism. Substantival monism is the view that reality is just one substance or self-existing thing or system, and that all things and events of daily experience are but parts or modifications of this ultimate substance. Besides "substantival" monism there is "at tributive" monism, that is the view that reality has but one irredu cible attribute. Now, attributive monism, as will be seen presently, may or may not be combined with substantival monism, and it may also be combined with substantival pluralism (the view that there is more than one ultimate substance). Idealistic monism combines substantival with attributive monism; Spinoza's monism combines substantival monism with attributive pluralism (that is the recognition of more than one irreducible attribute in ultimate reality) ; and the monodology of Leibnitz combines attributive monism with substantival pluralism. But to return to the main types of substantival monism. Differences in substantival monism must obviously be correlated with differences in the character attributed to the one ultimate reality which all forms of substan tival monism admit. Now the most familiar kinds of reality are those commonly described as the material and the mental (or body and mind, or extension and thought, etc.). Hence the most com mon differences in ontology, and therefore in substantival monism. are connected with these characters or attributes. The monism which identifies ultimate reality with matter or with physical energy is called materialism or energism or energetic monism. That which identifies it with mind or experience is called spiritual or psychical monism ; and if it identifies ultimate reality more par ticularly with reason or thought, it is called idealistic or intellec tualistic monism, and if with will, it is called voluntarism or volun tarist monism. Then there are varieties of monism which maintain
that ultimate reality is itself neither material nor psychical (or spiritual), and that it only expresses itself in these two parallel ways, and may be in many, or infinite other ways. These may be called dualistic or pluralistic forms of monism according 'as they combine attributive dualism or pluralism with substantival mon ism. But they are known by various other names, some of which and the reasons for them may be stated here. One name is agnostic monism, because the nature of ultimate reality is unknown, apart from its material and mental manifestations. Another name is neutral monism, because ultimate reality is regarded as being itself neither material nor mental, though expressing itself in both these ways. Sometimes it is called the identity philosophy or the mind stuff theory (q.v.), because the material and mental are regarded as having something identical or an identical source, or because the same ultimate entity is at once mind and matter. And so on. Before proceeding to other considerations it may be as well to note an important difference between these dualistic or pluralistic types of monism, on the one hand, and the materialistic and spiritualistic types, on the other. According to the former the material and the mental are equally real—neither is reducible to the other. Materialism, on the other hand, reduces the mental to a mere epiphenomenon (or by-product) of matter or physical energy; and idealistic or psychical monism reduces the material to a merely mental appearance. It is true, however, that even the dualistic or pluralistic types of monism show some of them a tendency to stress the mental side and so lean towards idealism, while others stress the material side and so lean towards material ism. The next ground of difference between types of monism turns on the answer to the question whether there is any pur posiveness in the processes of ultimate reality? If the answer is affirmative, we have teleological monism ; if negative we have either mechanistic or naturalistic monism. Lastly, there is the question of its divinity. If this is denied, we have atheistic monism ; if it is affirmed, as it is in the monism of Spinoza who identified Nature or the Universe (or Substance) with God, then we have pantheism or pantheistic monism.