Im`ma*te"ri*al*ism (?), n. [Cf. F. immatérialisme.] 1. The doctrine that immaterial substances or spiritual being exist, or are possible.

2. (Philos.) The doctrine that external bodies may be reduced to mind and ideas in a mind; any doctrine opposed to materialism or phenomenalism, esp. a system that maintains the immateriality of the soul; idealism; esp., Bishop Berkeley's theory of idealism.