The first of these displeasing propositions of psycho-analysis is this: that mental processes are essentially unconscious, and that those which are conscious are merely isolated acts and parts of the whole psychic entity. Now I must ask you to remember that, on the contrary, we are accustomed to identify the mental with the conscious. Consciousness appears to us as positively the characteristic that defines mental life, and we regard psychology as the study of the content of consciousness. This even appears so evident that any contradiction of it seems obvious nonsense to us, and yet it is impossible for psycho-analysis to avoid this contradiction, or to accept the identity between the conscious and the psychic. The psycho-analytical definition of the mind is that it comprises processes of the nature of feeling, thinking, and wishing, and it maintains that there are such things as unconscious thinking and unconscious wishing. But in doing so psycho-analysis has forfeited at the outset the sympathy of the sober and scientifically-minded, and incurred the suspicion of being a fantastic cult occupied with dark and unfathomable mysteries.[1] You yourselves must find it difficult to understand why I should stigmatize an abstract proposition, such as “The psychic is the conscious,” as a prejudice; nor can you guess yet what evolutionary process could have led to the denial of the unconscious, if it does indeed exist, nor what advantage could have been achieved by this denial. It seems like an empty wrangle over words to argue whether mental life is to be regarded as co-extensive with consciousness or whether it may be said to stretch beyond this limit, and yet I can assure you that the acceptance of unconscious mental processes represents a decisive step towards a new orientation in the world and in science. As little can you suspect how close is the connection between this first bold step on the part of psycho-analysis and the second to which I am now coming. For this next proposition, which we put forward as one of the discoveries of psycho-analysis, consists in the assertion that impulses, which can only be described as sexual in both the narrower and the wider sense, play a peculiarly large part, never before sufficiently appreciated, in the causation of nervous and mental disorders. Nay, more, that these sexual impulses have contributed invaluably to the highest cultural, artistic, and social achievements of the human mind.