There is another group of occurrences which is very closely related to errors but for which this name is not suitable. We call them ‘accidental’ and symptomatic acts. They also appear to be unmotivated, insignificant and unimportant but, in addition to this, they have very clearly the feature of superfluity. They are, on the one hand, distinguishable from errors by the absence of any second intention to which they are opposed and which they disturb; on the other hand, they merge without any definite line of demarcation into the gestures and movements which we regard as expressions of the emotions. To this class of accidental performances belong all those apparently purposeless acts which we carry out, as though in play, with clothing, parts of the body, objects within reach; also the omission of such acts; and again the tunes which we hum to ourselves. I maintain that all such performances have meaning and are explicable in the same way as are errors, that they are slight indications of other more important mental processes, and are genuine mental acts. I propose, however, not to linger over this further extension of the field of mental phenomena, but to return to the errors; for by a consideration of them problems of importance in the enquiry into psycho-analysis can be worked out much more clearly. Undoubtedly, the most interesting questions which we formulated while considering errors, and have not yet answered, are the following: We said that errors result from the mutual interference of two different intentions, of which one may be called the intention interfered with, and the other the interfering tendency. The intentions interfered with give rise to no further questions, but concerning the others we wish to know, first, what kind of intentions these are that arise as disturbers of others, and secondly, what are the relations between the interfering tendencies and those which suffer the interference? Allow me to take slips of the tongue again as representative of the whole series, and to answer the second question before the first. The interfering tendency in the slip of the tongue may be connected in meaning with the intention interfered with, in which case the former contains a contradiction of the latter, or corrects, or supplements it. Or, in other more obscure and more interesting cases, the interfering tendency may have no connection whatever in meaning with the intention interfered with.