Coherent thought is intermediate between the two extremes just mentioned. It is a train of thought regulated by the associative connections between all the separate ideas and one central idea which dominates and unifies the whole. The thought of a football game or of the destiny of the United States branches out into innumerable partial thoughts, each one leading to another one. But they are all united by their relation to this game or to this nation. Such a coherent thought need not possess a considerable length. Sometimes, as in unconstrained conversation or in letter writing, it may soon be followed by another coherent thought, this by a third, and so on, and these may be related to each other merely like the links of a chain. Sometimes, however, it lasts for hours, as in lecturing on a definite subject, or in writing or reading a chapter of a book or a whole book. Coherent thought depends largely on _memory_, on associative connections. But it depends also on those conditions which determine _attention_: unless the thoughts have an affective value, unless they are interesting to the individual in question, they are not likely to enter consciousness. Because of this dependence on the conditions of attention, certain persons are capable of coherent thought in some lines, but not in others. Whenever the purely _associative_ function predominates over the conditions of _attention_, or conversely, those abnormalities occur of which we have just spoken, mere chain-like thought, or obsession by a single idea. Nothing else favors coherent thought so much as the possession of language. The simplicity of a word or phrase and its connection with experiences of unlimited complexity enable the mind to keep within one system of thought in spite of temporary deviations, numerous and winding though they be. Such complicated ideas, inexhaustible to him who tries to describe them, as propriety, honor, duty, may guide and determine a long-continued train of thoughts and actions. The most important one of all these guiding ideas, crystallizing around a single word, is the idea of self, of _I_. 2. _The Self and the World_