As all sciences treat, to a great extent, of the same objects, they can be separated only according to _how_ they treat things. On this principle, Mr. Scripture divides sciences into Special Sciences, General or Philosophical Sciences, and Didactic Sciences. The Special sciences are, I, the Mathematical Sciences, treating the _forms_ of all experience; II, the Phenomenal Sciences, treating of the _contents_ of all experience; the second class is divided into the Physical Sciences, which treat experience from its objective side, and Mental Sciences, which treat experience from its subjective side. The group of Mental Sciences is best divided, according to Wundt’s scheme, into the sciences of mental processes, Psychological Sciences; the sciences of mental products, Philological Sciences; and the Sciences of mental development, Historical Sciences. Psychology as a science of mental phenomena has a two-fold relation to the physical sciences: it is complementary to them, a necessary auxiliary; they are complementary to it, accessories in psychological investigation. States of mind always remain states of mind; they cannot be resolved into motions of particles of matter, and it is a fundamental axiom that _mental phenomena cannot influence or be influenced by material phenomena_. But we are justified in talking about a nervous stimulation becoming a percept, a muscular contraction following an act of will, as long as we remember that these are only substitutes for unknown quantities. Physiology investigates nervous changes; Psychology, mental changes; Physiological Psychology, the relations between the two. Mental phenomena are of two kinds, mental processes and mental products. Psychology is the science of mental processes; it seeks the exact description and explanation of the operations of our inner experience. The relation of Psychology to Philosophy is a burning question. Metaphysics, or Philosophy in the narrower sense, seeks from the agreement of the results of all other sciences to establish a system of the principles that underlie all existence, i. e. a theory of the universe, material and mental. After the general principles have been determined by metaphysics, philosophy has the duty of correcting the special sciences when they set up one-sided hypotheses, and of helping where they are unable to proceed alone. Psychology is considered a part of philosophy, but as a special science, treating mental processes from its own standpoint, it is distinct from psychology as a general science treating mind, relations of mind and matter, etc., from the standpoint of philosophy. The latter should be termed Philosophical Psychology. The relation of Psychology to Logic depends on what the latter is. Logic is a science of thought, but thought is also a subject of psychology. Psychology treats thoughts as we think them; Logic, as we ought to think them. Each of the sciences, Epistemology, the doctrine of knowledge, and Methodology, the