I will expound to you those theoretical conceptions which alone have proved useful in giving greater definiteness to the term _repression_. For this purpose it is first necessary that we should proceed from the purely descriptive meaning of the word “unconscious” to its systematic meaning; that is, we resolve to think of the consciousness or unconsciousness of a mental process as merely one of its qualities and not necessarily definitive. Suppose that a process of this kind has remained unconscious, its being withheld from consciousness may be merely a sign of the fate it has undergone, not necessarily the fate itself. Let us suppose, in order to gain a more concrete notion of this fate, that every mental process—there is one exception, which I will go into later—first exists in an unconscious state or phase, and only develops out of this into a conscious phase, much as a photograph is first a negative and then becomes a picture through the printing of the positive. But not every negative is made into a positive, and it is just as little necessary that every unconscious mental process should convert itself into a conscious one. It may be best expressed as follows: Each single process belongs in the first place to the unconscious psychical system; from this system it can under certain conditions proceed further into the conscious system. The crudest conception of these systems is the one we shall find most convenient, a spatial one. The unconscious system may therefore be compared to a large ante-room, in which the various mental excitations are crowding upon one another, like individual beings. Adjoining this is a second, smaller apartment, a sort of reception-room, in which, too, consciousness resides. But on the threshold between the two there stands a personage with the office of door-keeper, who examines the various mental excitations, censors them, and denies them admittance to the reception-room when he disapproves of them. You will see at once that it does not make much difference whether the door-keeper turns any one impulse back at the threshold, or drives it out again once it has entered the reception-room; that is merely a matter of the degree of his vigilance and promptness in recognition. Now this metaphor may be employed to widen our terminology. The excitations in the unconscious, in the antechamber, are not visible to consciousness, which is of course in the other room, so to begin with they remain unconscious. When they have pressed forward to the threshold and been turned back by the door-keeper, they are ‘_incapable of becoming conscious_’; we call them then _repressed_. But even those excitations which are allowed over the threshold do not necessarily become conscious; they can only become so if they succeed in attracting the eye of consciousness. This second chamber therefore may be suitably called _the preconscious system_. In this way the process of becoming conscious retains its purely descriptive sense.