The question what significance those factors, which some writers have placed in the foreground, can now have for us—such factors as disturbances of the circulation, fatigue, excitement, distraction, disturbances of attention—demands a more exhaustive reply if we assume the mental mechanism of slips described above. You will notice that we do not deny these factors. Indeed, in general it doesn’t often happen that psycho-analysis contests anything which is maintained in other quarters; as a rule, psycho-analysis only adds something new to what has been said; and it does certainly happen on occasion that what has hitherto been overlooked, and is now supplied by psycho-analysis, is the most essential part of the matter. The influence of such physiological predispositions as arise in slight illness, circulatory disturbances and conditions of fatigue, upon the occurrence of slips of the tongue is to be admitted without more ado; everyday personal experience may convince you of it. But how little is explained by this admission! Above all, these are not necessary conditions of errors. Slips of the tongue may just as well occur in perfect health and normal conditions. These bodily factors, therefore, are merely contributory; they only favour and facilitate the peculiar mental mechanism which produces slips of the tongue. I once used an illustration for this state of things which I will repeat here, as I know of no better. Just suppose that on some dark night I am walking in a lonely neighbourhood and am assaulted by a rogue who seizes my watch and money, whereupon, since I could not see the robber’s face clearly, I make my complaint at the police-station in these words: “Loneliness and darkness have just robbed me of my valuables.” The police officer might reply to me: “You seem to carry your support of the extreme mechanistic point of view too far for the facts. Suppose we put the case thus: Under cover of darkness and encouraged by the loneliness of the spot, some unknown thief has made away with your valuables. It appears to me that the essential thing to be done is to look about for the thief. Perhaps we shall then be able to take the plunder from him again.”