=Nature of Thinking.=--In the study of general method, as well as in that of the foregoing mental processes, it has been taken for granted that our minds are capable of identifying different objects on the basis of some common feature or features. This tendency of the mind to identify objects and group individual things into classes, depends upon its capacity to detect similarity and difference, or to make comparisons. When the mind, in identifying objects, events, qualities, etc., discovers certain relations between its various states, the process is especially known as that of thinking. In its technical sense, therefore, thought implies a more or less explicit apprehension of relation.
=Thinking Involved in all Conscious States.=--It is evident, however, that every mental process must involve thinking, or a grasping of relations. When, by my merely touching an object, my mind perceives it is an apple, this act of perception, as already seen, takes place because elements of former experience come back as associated factors. This implies, evidently, that the mind is here relating elements of its past experience with the present touch sensation. Perception of external objects, therefore, implies a grasping of relations. In the same way, if, in having an experience to-day, one recognizes it as identical with a former experience, he is equally grasping a relation. Every act of memory, therefore, implies thinking. Thus in all forms of knowledge the mind is apprehending relations; for no experience could have meaning for the mind except as it is discriminated from other experiences. In treating thinking as a distinct mental process, however, it is assumed that the objects of sense perception, memory, etc., are known as such, and that the mind here deals more directly with the relations in which ideas stand one to another. As a mental process, thinking appears in three somewhat distinct forms, known as conception, judgment, and reasoning.
=The Abstract Notion.=--It was seen that at least in adult life, the perception of any object, as this particular orange, horse, cow, etc., really includes a number of distinct images of quality synthesised into the unity of a particular idea or experience. Because of this union of a number of different sensible qualities in the notion of a single individual, the mind may limit its attention upon a particular quality, or characteristic, possessed by an object, and make this a distinct problem of attention. Thus the mind is able to form such notions as length, roundness, sweetness, heaviness, four-footedness, etc. When such an attribute is thought of as something distinct from the object, the mental image is especially known as an abstract idea, or notion, and the process as one of abstraction.