The part of the mental apparatus, which is the seat of consciousness, is originally no different in nature from the part where memories (“facilitations”) are laid down. It also consists of elements separated by resistances, which incoming excitations have to overcome. However, consciousness occurs on the surface of the system, where incoming excitation makes its first contact with the resistances between elements. So the excitation is as yet undiminished by the effort, which it will have to expend in order to overcome ever more resistance on its journey into the system, and, as a result, the resistances between elements in the surface layer are entirely swept away instead of only being “tyre-marked” like those further in. Why, it may well be asked, should this destruction of resistance produce consciousness? All that Freud has to say is that “the elements of the system Cs. [the consciousness system] would carry no bound energy but only energy capable of free discharge” (1920g: 26-27). Because there are no resistances, excitation flows freely, and this free flow is consciousness.
Freud then suddenly advances the idea that trauma occurs precisely when the whole of the mental apparatus is flooded by an inrush of excitation from the outside world, which has broken through a “protective shield“ around it (more of this shield in a minute) and which the apparatus is unable to “bind” i.e., when there is uncontrolled free flow of excitation in the apparatus. He suggests that the phenomena of repetition, which he had discussed in sections 1-3, are just the efforts of the apparatus to bind that free flow (1920g: 30).
Three things in Freud’s whistle-stop tour of what appear initially to be disparate ideas are striking. First, the idea of consciousness as free flow has poetic appeal, but it is unclear what to make of it as a scientific, psychological theory of consciousness. Second, Freud pirouettes from a discussion of consciousness to his proposal regarding the nature of trauma via the concept of excitation that is in free flow (that is “unbound”). Both consciousness and trauma are generated by unbound