In the theory of psycho-analysis we have no hesitation in assuming that the course taken by mental events is automatically regulated by the pleasure principle. We believe, that is to say, that the course of those events is invariably set in motion by an unpleasurable tension, and that it takes a direction such that its final outcome coincides with a lowering of that tension—that is, with an avoidance of unpleasure or a production of pleasure. In taking that course into account in our consideration of the mental processes which are the subject of our study, we are introducing an 'economic' point of view into our work; and if, in describing those processes, we try to estimate this 'economic' factor in addition to the 'topographical' and 'dynamic' ones, we shall, I think, be giving the most complete description of them of which we can at present conceive, and one which deserves to be distinguished by the term 'metapsychological'.

It is of no concern to us in this connection to enquire how far, with this hypothesis of the pleasure principle, we have approached or adopted any particular, historically established, philosophical system. We have arrived at these speculative assumptions in an attempt to describe and to account for the facts of daily observation in our field of study. Priority and originality are not among the aims that psycho-analytic work sets itself; and the impressions that underlie the hypothesis of the pleasure principle are so obvious that they can scarcely be overlooked. On the other hand we would readily express our gratitude to any philosophical or psychological theory which was able to inform us of the meaning of the feelings of pleasure and unpleasure which act so imperatively upon us. But on this point we are, alas, offered nothing to our purpose. This is the most obscure and inaccessible region of the mind, and, since we cannot avoid contact with it, the least rigid hypothesis, it seems to me, will be the best. We have decided to relate pleasure and unpleasure to the quantity of excitation that is present in the mind but is not in any way 'bound'; and to relate them in such a manner that unpleasure corresponds to an increase in the quantity of excitation and pleasure to a diminution. What we are implying by this is not a simple relation between the strength of the feelings of pleasure and unpleasure and the corresponding modifications in the quantity of excitation; least of all—in view of all we have been taught by psycho-physiology—are we suggesting any directly proportional ratio: the factor that determines the feeling is probably the amount of increase or diminution in the quantity of excitation in a given period of time. Experiment might possibly play a part here; but it is not advisable for us analysts to go into the problem further so long as our way is not pointed by quite definite observations.

We cannot, however, remain indifferent to the discovery that an investigator of such penetration as G. T. Fechner held a view on the subject of pleasure and unpleasure which coincides in all essentials with the one that has been forced upon us by psycho-analytic work. Fechner's statement is to be found contained in a small work, Einige Ideen zur Schöpfungs- und Entwicklungsgeschichte der Organismen, 1873 (Part XI, Supplement, 94), and reads as follows: 'In so far as conscious impulses always have some relation to pleasure or unpleasure, pleasure and unpleasure too can be regarded as having a psycho-physical relation to conditions of stability and instability. This provides a basis for a hypothesis into which I propose to enter in greater detail elsewhere. According to this hypothesis, every psycho-physical motion rising above the threshold of consciousness is attended by pleasure in proportion as, beyond a certain limit, it approximates to complete stability, and is attended by unpleasure in proportion as, beyond a certain limit, it deviates from complete stability; while between the two limits, which may be described as qualitative thresholds of pleasure and unpleasure, there is a certain margin of aesthetic indifference...."

The facts which have caused us to believe in the dominance of the pleasure principle in mental life also find expression in the hypothesis that the mental apparatus endeavours to keep the quantity of excitation present in it as low as possible or at least to keep it constant. This latter hypothesis is only another way of stating the pleasure principle; for if the work of the mental apparatus is directed towards keeping the quantity of excitation low, then anything that is calculated to increase that quantity is bound to be felt as adverse to the functioning of the apparatus, that is as unpleasurable.

The pleasure principle follows from the principle of constancy: actually the latter principle was inferred from the facts which forced us to adopt the pleasure principle. Moreover, a more detailed discussion will show that the tendency which we thus attribute to the mental apparatus is subsumed as a special case under Fechner's principle of the 'tendency towards stability', to which he has brought the feelings of pleasure and unpleasure into relation.

It must be pointed out, however, that strictly speaking it is incorrect to talk of the dominance of the pleasure principle over the course of mental processes. If such a dominance existed, the immense majority of our mental processes would have to be accompanied by pleasure or to lead to pleasure, whereas universal experience completely contradicts any such conclusion. The most that can be said, therefore, is that there exists in the mind a strong tendency towards the pleasure principle, but that that tendency is opposed by certain other forces or circumstances, so that the final outcome cannot always be in harmony with the tendency towards pleasure. We may compare what Fechner (1873, 90) remarks on a similar point: 'Since however a tendency towards an aim does not imply that the aim is attained, and since in general the aim is attainable only by approximations....'

If we turn now to the question of what circumstances are able to prevent the pleasure principle from being carried into effect, we find ourselves once more on secure and well-trodden ground and, in framing our answer, we have at our disposal a rich fund of analytic experience.

The first example of the pleasure principle being inhibited in this way is a familiar one which occurs with regularity. We know that the pleasure principle is proper to a primary method of working on the part of the mental apparatus, but that, from the point of view of the self-preservation of the organism among the difficulties of the external world, it is from the very outset inefficient and even highly dangerous. Under the influence of the ego's instincts of self-preservation, the pleasure principle is replaced by the reality principle. This latter principle does not abandon the intention of ultimately obtaining pleasure, but it nevertheless demands and carries into effect the postponement of satisfaction, the abandonment of a number of possibilities of gaining satisfaction and the temporary toleration of unpleasure as a step on the long indirect road to pleasure. The pleasure principle long persists, however, as the method of working employed by the sexual instincts, which are so hard to 'educate', and, starting from those instincts, or in the ego itself, it often succeeds in overcoming the reality principle, to...