Monism: Although the term was first used by German philosopher Christian Wolff (1679-1754), monism is a philosophical position with a long history dating back to the pre-Socratic philosophers who appealed to a single unifying principle to explain all the diversity of observed experience. Notable among these thinkers is Parmenides, who maintained that reality is an undifferentiated oneness, or unity, and the consequently real change or individuality of things is impossible. Monism is a position taken on the metaphysical question, “How many things are there?”
Substantival monism (“one thing”) is the view that there is only one substance and that all diversity is ultimately unreal. This view was maintained by Spinoza, who claimed that there is only one substance, or independently existing thing, and that both God and the universe are aspects of this substance.
Attributive monism (“one category”) holds that there is one kind of thing but many different individual things in this category. Materialism and idealism are different forms of attributive monism. The materialist holds that the one category of existence in which all real things are found is material, while the idealist says that this category is mental. All monisms oppose the dualistic view of the universe, which holds that both material and immaterial (mental and spiritual) realities exist.
 Walter A. Elwell, Evangelical dictionary of theology (Grand Rapids, Mich.: Baker Book House, 1984), 730. Print.