Mentalism is the idea that only mind or spirit really exists, or that mind or spirit is the fundamental substance in the universe. Mentalism is sometimes called immaterialism, and is usually held to be similar to or equivalent to idealism . Modernism is usually an aesthetic variety of subjectivism . Monism is an answer offered to philosophical dualism by adherents of idealism and by adherents of materialism . Monotheism is the belief there is only one god, or that the gods of different religions are really just different manifestations of the one true god.
Monotheism is opposed to both henotheism and polytheism .
When people refer to a similar view in philosophy proper, they usually use some other word, for example irrationalism in epistemology and intuitionism in ethics.