That errors have a meaning we may certainly set down as established by our efforts up to this point, and may take this conclusion as a basis for our further investigations. Let me once more emphasize the fact that we do not maintain—and for our purposes do not need to maintain—that every single mistake which occurs has a meaning, although I think that probable. It is enough for us to prove that such a meaning is relatively frequent in the various forms of errors. In this respect, by the way, the various forms show certain differences. Some cases of slips of the tongue, slips of the pen, and so on, may be the effect of a purely physiological cause, though I cannot believe this possible of those errors which depend upon forgetfulness (forgetting of names or intentions, mislaying, and so on); losing possessions is in all probability to be recognized as unintentional in some cases; altogether our conceptions are only to a certain extent applicable to the mistakes which occur in daily life. These limitations should be borne in mind by you when we proceed on the assumption that errors are mental acts arising from the mutual interference of two intentions. This is the first result of our psycho-analysis. Hitherto psychology has known nothing of such interferences or of the possibility that they could occasion manifestations of this kind. We have widened the domain of mental phenomena to a very considerable extent and have won for psychology phenomena which were never before accredited to it. Let us dwell for a moment on the proposition that errors are “mental acts.” Does this mean any more than our former statement, that they have a meaning? I do not think so; on the contrary, it is a more indefinite statement and one more open to misunderstanding. Everything that can be observed in mental life will be designated at one time or another as a mental phenomenon. It depends, however, whether the particular mental phenomenon is directly due to bodily, organic or material agencies, in which case it does not fall to psychology for investigation; or whether it arose directly from other mental processes, behind which at some point the succession of organic agencies then begins. We have in mind the latter state of things when we describe a phenomenon as a mental process, and it is therefore more expedient to put our statement in this form: The phenomenon has meaning; and by meaning we understand significance, intention, tendency and a position in a sequence of mental concatenations.