But beneath our stream of consciousness lies a deep sea of memories, feelings, and directive influences. All our previous experience is buried there, and no man knows how much he knows. Every one has experienced the sudden recollections which come up unsought when a sight, a sound, or a scent makes association with something long past and apparently forgotten; and not only our memories of things, places, and people, but our past mental processes themselves lie in this deep sea of the _unconscious_, to help or hinder us in the present or future. I speak of the unconscious, though there are objections to the use of the word, which may lead to such a contradiction of terms as 'unconscious knowledge'. It is much more than a storehouse of memories: it is the seat of mental processes which take place unknown to us and are revealed at times in strange and unexpected ways. It comes into contact with the stream of consciousness, and, as we so often find in attempting to classify natural phenomena, there are no well-marked lines of demarcation between one and the other, though the extremes are definite enough. The unconscious is not always a willing servant and often refuses to obey the wishes of its owner. Every one has at some time vainly tried to recall a name which is 'on the tip of the tongue', and one name after another is tried till perhaps the right one comes up and leaves us wondering where the difficulty was. There is, according to the teaching of some psychologists, always a reason for this failure to remember, though even an apparently ordinary example may need a skilful analysis to show how the failure arose and why the other names presented themselves. Slips of the tongue are likewise dependent upon unconscious influences, and, although I was once sceptical, a few examinations of my own slips have convinced me of the truth of this little theory. Here is an example of one of them, such as occurs often enough and would ordinarily be passed over without further examination:--