§ 101. Reminding ourselves anew that philosophical problems cannot be treated in isolation from one another, we shall hereinafter seek to become acquainted with general stand-points that give systematic unity to the issues which have been enumerated. Such stand-points are not clearly defined by those who occupy them, and they afford no clear-cut classification of all historical philosophical philosophies. But system-making in philosophy is commonly due to the moving in an individual mind of some most significant idea; and certain of these ideas have reappeared so frequently as to define more or less clearly marked tendencies, or continuous strands, out of which the history of thought is forever weaving itself. Such is clearly the case with _naturalism_. From the beginning until now there have been men whose philosophy is a summation of the natural sciences, whose entire thought is based upon an acceptance of the methods and the fundamental conceptions of these disciplines. This tendency stands in the history of thought for the conviction that the visible and tangible world which interacts with the body is veritable reality. This philosophy is realistic and empirical to an extent entirely determined by its belief concerning being. But while naturalism is only secondarily epistemological, _subjectivism_ and _absolute idealism_ have their very source in the self-examination and the self-criticism of thought. Subjectivism signifies the conviction that the knower cannot escape himself. If reality is to be kept within the range of possible knowledge, it must be defined in terms of the processes or states of selves. _Absolute idealism_ arises from a union of this epistemological motive with a recognition of what are regarded as the logical necessities to which reality must submit. Reality must be both knowledge and rational knowledge; the object, in short, of an absolute mind, which shall be at once all-containing and systematic. This rationalistic motive was, however, not originally associated with an idealistic epistemology, but with the common-sense principle that being is discovered and not constituted by thought. Such an _absolute realism_ is, like naturalism, primarily metaphysical rather than epistemological; but, unlike naturalism, it seeks to define reality as a logical or ethical necessity. Under these several divisions, then, we shall meet once more with the special problems of philosophy, but this time they will be ranged in an order that is determined by some central doctrine. They will appear as parts not of the general problem of philosophy, but of some definite system of philosophy. FOOTNOTES: [180:1] Cf. § 68. [182:2] The Socratic distinction between the logical and the psychological treatment of belief finds its best expression in Plato's _Gorgias_, especially, 454, 455. Cf. also § 29. [182:3] Thus, e. g. Hegel. See § 179. Cf. also §§ 199, 200. [183:4] Cf. § 84. [184:5] See § 69, _note_.