The fruitfulness of the philosopher's reflective doubt concerning his own powers is now evident. Problems are raised which are not merely urgent in themselves, but which present wholly new alternatives to the metaphysician. Rationalism and empiricism, realism and idealism, are doctrines which, though springing from the epistemological query concerning the possibility of knowledge, may determine an entire philosophical system. They bear upon every question of metaphysics, whether the fundamental conception of being, or the problems of the world's unity, origin, and significance for human life. FOOTNOTES: [150:1] The post-Kantian movement in Germany--especially in so far as influenced by Hegel. See Chap. XII. [151:2] Cf. § 203. [152:3] _E. g._, the system of Fichte. Cf. § 177. [153:4] See Chap. XI. [153:5] Spinoza: _On the Improvement of the Understanding_. Translation by Elwes, p. 3. [154:6] Spinoza: _Ethics_, Part V, Proposition XLII. Translation by Elwes, p. 270. [155:7] Descartes: _Meditations_, I. Translation by Veitch, p. 97. [155:8] Leibniz: _New System of the Nature of Substances_. Translation by Latta, pp. 299, 300. [157:9] Burnet: _Early Greek Philosophy_, p. 42. [159:10] No little ambiguity attaches to the term "monism" in current usage, because of its appropriation by those who maintain that the universe is unitary and homogeneous in _physical terms_ (cf. § 108). It should properly be used to emphasize the unity of the world in any terms. [161:11] Burnet: _Op. cit._, p. 358. [162:12] Burnet: _Op. cit._, p. 284. [167:13] Plato: _Theætetus_, 161. Translation by Jowett. References to Plato are to the marginal paging. [168:14] Burnet: _Early Greek Philosophy_, pp. 184, 187. [171:15] Plato: _Theætetus_, 150 B. Translation by Jowett. [173:16] Much ambiguity attaches to the terms "realism" and "idealism" in current usage. The first had at one time in the history of philosophy a much narrower meaning than that which it now possesses. It was used to apply to those who, after Plato, believed in the independent reality of ideas, universals, or general natures. _Realists_ in this sense were opposed to _nominalists_ and _conceptualists_. Nominalism maintained the exclusive reality of individual substances, and reduced ideas to particular signs having, like the _name_, a purely symbolical or descriptive value. Conceptualism sought to unite realism and nominalism through the conception of mind, or an individual substance whose meanings may possess universal validity. Though this dispute was of fundamental importance throughout the mediæval period, the issues involved have now been restated. Realism in the old sense will, if held, come within the scope of the broader epistemological realism defined above. Nominalism is covered by empirical tendencies, and conceptualism by modern idealism.