In psychological experiments, fatigue _lowers the level and lessens the duration of attention_, and so, like habituation, makes against discrimination; unlike habituation, it tends also to _inhibit expression_, and thus renders the observer’s report hesitating and uncertain. It is characterised, unlike practice and habituation both, by a special mental complex; a diffused feeling of lassitude which may be dominated by some local strain or pain. In conclusion, we may mention that a great deal of controversy has centred about the questions _whether special practice has a general or a merely local effect_, and _whether general fatigue may be estimated from the results of some special and local test_. The first question may be answered in the words of Professor Thorndike: “One mental function or activity improves others in so far as and because they are in part identical with it, because it contains elements common to them. These identical elements may be in the stuff, the data concerned in the training, or in the attitude, the method taken with it.” The second question cannot yet be answered. We have every reason to think that fatigue is everywhere and always one and the same state, that mental and muscular fatigue, for instance, are identical; if we are mentally fatigued, we get rest neither by a change of mental work nor by physical exertion. But no single test or index of the danger-point of fatigue has yet been discovered. Questions and Exercises (1) Criticise the following statements. (A good plan would be, first, to go behind the expression to the meaning, and to make sure of that; then to take up precisely the opposite position, and see what can be said for it; and then finally to write your comments on the statements themselves.) (_a_) When two elementary brain-processes have been active together or in immediate succession, one of them, on reoccurring, tends to propagate its excitement into the other. (_b_) There is no tendency on the part of _simple_ ‘ideas,’ attributes, or qualities to remind us of their like, (_c_) Association marries only universals. (_d_) Brick is one complex idea, mortar is another complex idea; these ideas, with ideas of position and quantity, compose my idea of a wall. W. James, Principles of Psychology, i., 1890, 566, 579; F. H. Bradley, in Mind, xii., 1887, 358; J. Mill, Analysis of the Phenomena of the Human Mind, i., 1869, 115. (2) How does the dominance of associationism in British psychology throw light upon the psychology of the nation itself? (3) What sort of service could the doctrine of association render to psychology? (4) Can you give specific reasons for the fact that too long a series of syllables throws the learner into confusion? and for the advantage that results from distribution of the series in time? (5) Do you think that the quick or the slow learner has the better chance to retain what he has learned? Have you any evidence?