=Deals with Former Experiences.=--This mental organizing, or unifying, of the elements of past experiences to secure control of the new experience, is usually spoken of as a process of synthesis. The term synthesis, however, must be used with the same care as was noted in regard to the term analysis. Synthesis does not mean that totally _new_ elements are being unified, but merely that whatever selected elements of old knowledge the mind is able to read into a presented problem, are built, or organized, into a new system; and constitute, for the time being, one's knowledge and control of that problem. This is well exemplified by noting the growth of a person's knowledge of any object or topic. Thus, so long as the child is able to apperceive only the three sides and three angles of a triangle, his idea of triangle includes a synthesis of these. When later, through the building up of his geometric knowledge, he is able to apperceive that the interior angles equal two right angles, his knowledge of a triangle expands through the synthesis of this with the former knowledge. =All Knowledge a Synthesis.=--The fact that all knowledge is an organization from earlier experiences becomes evident by looking at the process from the other direction. The adult who has complete knowledge of an orange has it as a single experience. This experience is found, however, to represent a co-ordination of other experiences, as touch, taste, colour, etc. Moreover, each of these separate characteristics is an association of simpler experiences. Experiencing the touch of the orange, for instance, is itself a complex made up of certain muscular, touch, and temperature sensations. From this it is evident that the knowledge of an orange, although a unity of experience in adult life, is really a complex, or synthesis, made up of a large number of different elements.