The Principles of Psychology (1890) by William James was an influential textbook that summarized major achievements in psychology at that time. This book was unprecedented in its presentation of phenomenology of mental life in its richness, singularity, and complexity. However, much of the book’s content is now outdated.

James sees his task in studying our “original sensible totals,” (1.1.487), researching what mental facts in their totality are and how they relate to the physiological processes behind them. In his pursuit, James follows an analytical method of introspection. This method is applied both to personal experience, which is gained naturally, and purposely arranged situations.

James’s research proceeds from the presupposition about the existence a the material world which is independent of our consciousness. However, he does not want to say that man’s inner world is a sort of counterpart of the outward reality embedded in our consciousness.

His approach is usually associated with functionalism in American psychology. This school emphasizes practical reason, action, and personal achievement, as well as seeking effective ways to adapt to a changing situation.

James gives a distinctive interpretation of consciousness. He writes about the stream of thought, of consciousness, or of subjective life, stressing a process character of mental facts and perceiving them as unique states that constantly change. While structuralists view consciousness as a sum of separate elements, James discusses of the stream of thought as of uninterrupted dynamic continuity.

Consciousness, then, does not appear to itself chopped up in bits. Such words as "chain" or "train" do not describe it fitly as it presents itself in the first instance. It is nothing jointed; if flows. A "river" or a "stream" are the metaphors by which it is most naturally described. In talking of it hereafter, let us call it the stream of thought, of consciousness, or of subjective life. (1.1.239)

Another important characteristic of consciousness is its being selective: it always selects some states while rejecting others. James refers to the main defining processes of selection: attention and habit. He spends much time discussing the process of categorization of information coming in from the outward world.

In a chapter on the Self, James advocates a broad definition of it. Important are not only its constituents, but also “the feelings and emotions they arouse” as well as “the actions to which they prompt” (1.1.252).

One of the most notable of James’s contributions is his theory of emotions. Organic processes are considered to be the direct cause, source, and essence of emotion. Says he:

we feel sorry because we cry, angry because we strike, afraid because we tremble, and not that we cry, strike, or tremble, because we are sorry, angry, or fearful, as the case may be. (1.2.450)

In many instances in his book, James disavows himself from the philosophy of materialism. Nevertheless, one cannot say that he breaks free from materialism entirely. At least, he recognizes the existence of the material world which is independent of our consciousness. As for the soul, he presents it as an entity which is in a sense separate from the material world. While it is true that James, as a psychologist, relegates proving the existence of the soul to theology, concentrating on the investigation of mental facts, he is not always successful in separating psychology from metaphysics. On many particular points, James’s position is not materialistic.