A few words will suffice to define our problem and classify its elements. Where and when does philosophy begin? Manifestly, according to the analysis made in § I., where a final philosophical principle, a final ground of being is first sought in a philosophical way,—and hence with the Grecian philosophy. The Oriental—Chinese and Hindoo—so named philosophies,—but which are rather theologies or mythologies,—and the mythic cosmogonies of Greece, in its earliest periods, are, therefore, excluded from our more definite problem. Like Aristotle, we shall begin the history of philosophy with Thales. For similar reasons we exclude also the philosophy of the Christian middle ages, or Scholasticism. This is not so much a philosophy, as a philosophizing or reflecting within the already prescribed limits of positive religion. It is, therefore, essentially theology, and belongs to the science of the history of Christian doctrines. The material which remains after this exclusion, may be naturally divided into two periods; viz:—ancient—Grecian and Græco-Romanic—and modern philosophy. Since a preliminary comparison of the characteristics of these two epochs could not here be given without a subsequent repetition, we shall first speak of their inner relations, when we come to treat of the transition from the one to the other. The first epoch can be still farther divided into three periods; (1.) The pre-Socratic philosophy, _i. e._ from Thales to the Sophists inclusive; (2.) Socrates, Plato, Aristotle; (3.) The post-Aristotelian philosophy, including New Platonism. SECTION III. GENERAL VIEW OF THE PRE-SOCRATIC PHILOSOPHY. 1. The universal tendency of the pre-Socratic philosophy is to find some principle for the explanation of nature. Nature, the most immediate, that which first met the eye and was the most palpable, was that which first aroused the inquiring mind. At the basis of its changing forms,—beneath its manifold appearances, thought they, lies a first principle which abides the same through all change. What then, they asked, is this principle? What is the original ground of things? Or, more accurately, what element of nature is the fundamental element? To solve this inquiry was the problem of the _Ionic_ natural philosophers. One proposes as a solution, water, another, air, and a third, an original chaotic matter.