The process of clarification may be reversed, and the act of forgetting is such a reversal. This may take a considerable time, and is usually noticed only by accident at some point or other of its course. The process is similar to the gradual obliteration of well-made roads, for the maintenance of which no provision has been made. The faint anticipations of a thought are very like the faint recollections of it, and the latter gradually become blurred as in the case of a neglected road over the boundaries of which animals stray, slowly obliterating it. In this connection a practical rule for memorising, discovered and applied by a friend of mine, is interesting. It generally happens that if one wants to learn, say, a piece of music, or a section from the history of philosophy, one has to go over parts of it again and again. The problem was, how long should the intervals be between these successive attempts to commit to memory? The answer was that they should not be so long as to make it possible to take a fresh interest in the subject again, to be interested and curious about it. If the interval has produced that state of mind, then the process of clarification must begin from the beginning again. The rather popular physiological theory of Sigismund Exner as to the formation of “paths” in the nervous system may perhaps be taken as a physical parallel of the process of clarification. According to the theory, the nerves, or rather the fibrils, make paths easy for the stimulations to travel along, if these stimulations last sufficiently long or are repeated sufficiently often. So also in the case of forgetting; what happens is that these paths or processes of the nerve-cells atrophy from disuse. Avenarius would have explained the above processes by his theory of the articulation of the fibres of the brain, but his physical doctrine was rather too crude and too simple for application to psycho-physics. None the less his conception of articulation or jointing is both convenient and appropriate in its application to the process of clarification, and I shall employ it in that connection. The process of clarification must be traced thoroughly in order to realise its importance, but for the moment, it is important to consider only the initial stage. The distinction of Avenarius between “element” and “character,” which later on will become evident in a process of clarification, is not applicable to the very earliest moments of the process. It is necessary to coin a name for those minds to which the duality of element and character becomes appreciable at no stage of the process. I propose for psychical data at this earliest stage of their existence the word Henid (from the Greek ἑν, because in them it is impossible to distinguish perception and sensation as two analytically separable factors, and because, therefore, there is no trace of duality in them).