What is true of our idea of an orange is true of every other idea. Whether it be the understanding of a plant, an animal, a city, a picture, a poem, an historical event, an arithmetical problem, or a scientific experiment, the process is always the same. The apperceptive process of interpreting the new by selecting and relating elements of former experience, or the process of analysis-synthesis, is universal in learning. Expressed in another form, what is at first indistinct and indefinite becomes clear and defined through attention selecting, for the interpretation of the new presentation, suitable old ideas and setting up relationships among them. Analysis, or selection, is incomplete without an accompanying unification, or synthesis; synthesis, or organization, is impossible without analysis, or selection. It is on account of the mind's ability to unify a number of mental factors into a single experience, that the process of unification, or synthesis, is said to imply economy within our experiences. This fact will become even more evident, however, when later we study such mental processes as sense perception and conception. INTERACTION OF PROCESSES It is to be noted, however, that the selecting and the relating of the different interpreting ideas during the learning process are not necessarily separate and distinct parts of the lesson. In other words, the mind does not first select out of its former knowledge a whole mass of disconnected elements, and then later build them up into a new organic experience. There is, rather, in almost every case, a continual interplay between the selecting and relating activity, or between analysis and synthesis, throughout the whole learning process. As soon, for instance, as a certain feature, or characteristic, is noted, this naturally relates itself to the central problem. When later, another characteristic is noted, this may relate itself at once both with the topic and with the formerly observed characteristic into a more complete knowledge of the object. Thus during a lesson we find a gradual growth of knowledge similar to that illustrated in the case of the scholar's knowledge of the triangle, involving a continual interplay of analysis and synthesis, or of selecting and relating different groups of ideas relative to the topic. This would he illustrated by noting a pupil's study of the cat. The child may first note that the cat catches and eats rats and mice, and picks meat from bones. These facts will at once relate themselves into a certain measure of knowledge regarding the food of the animal. Later he may note that the cat has sharp claws, padded feet, long pointed canines, and a rough tongue; these facts being also related as knowledge concerning the mouth and feet of the animal. In addition to this, however, the latter facts will further relate themselves to the former as cases of adaptation, when the child notes that the teeth and tongue are suited to tearing food and cleaning it