The term "feeling," as used in this connection in psychology, has been defined as "the simple _agreeable_ or _disagreeable_ side of any mental state." These agreeable or disagreeable sides of mental states are quite distinct from the act of knowing, which accompanies them. One may perceive and thus "know" that another is speaking to him and be fully aware of the words being used and of their meaning. Ordinarily, and so far as pure thought processes are concerned, this would complete the mental state. But we must reckon on the feeling side as well as on the thinking side of the mental state. Accordingly we find that the knowledge of the words of the other person and the meaning thereof results in a mental state agreeable or disagreeable. In the same way the reading of the words of a book, the hearing of a song, or a sight or scene perceived, may result in a more or less strong feeling, agreeable or disagreeable. This sense of agreeable or disagreeable consciousness is the essential characteristic of what we call "feeling." It is very difficult to explain feeling except in its own terms. We know very well what we mean, or what another means, when it is said that we or he "_feels_ sad," or has "a joyous feeling," or "a feeling of interest." And yet we shall find it very hard to explain the mental state except in terms of feeling itself. Our knowledge depends entirely upon our previous experience of the feeling. As an authority says: "If we have never felt pleasure, pain, fear, or sorrow, a quarto volume cannot make us understand what such a mental state is." Every mental state is not distinguished by strong feeling. There are certain mental states which are concerned chiefly with intellectual effort, and in which all trace of feeling seems to be absent, unless, as some have claimed, the "feeling" of interest or the lack of same is a faint form of the feeling of pleasure or pain. Habit may dull the feeling of a mental state until it is apparently neutral, but there is generally a faint feeling of like or dislike still left. The elementary forms of feeling are closely allied with those of simple sensation. But experiments have revealed that there is a distinction in consciousness. It has been discovered that one is often conscious of the "touch" of a heated object before he is of the feeling or pain resulting from it. Psychologists have pointed out another distinction, namely: When we experience a sensation we are accustomed to refer it to the outside thing which is the object of it, as when we touch the heated object; but when we experience a feeling we instinctively refer it to ourself, as when the heated object gives us pain. As an authority has said: "My feelings belong to me; but my sensations seem to belong to the object which caused them."