In the brief description which I have now given of our mental processes, I have for the most part avoided certain terms which are current in the science of psychology. It will be well here to say a few words concerning these words and their use. The process of _sensation_ is sometimes defined as the mere reception of a sense-stimulus. But it is more convenient, and more in accordance with common usage, to call the simple result of a stimulus an impression, and to apply the term "sensation" to the discrimination and recognition of the impressions as of such and such a quality. Sensation, then, is the reception and discrimination of impressions which result from certain modes of influence (stimuli) brought to bear on our organization. Viewed in this way, therefore, even sensation involves a distinct reaction of the mind; it implies the first stage of mental activity. But when the sensations are given objective significance, when they suggest the existence of an object-world without us, they enter the field of _perception_. Here the discriminated sense-impression is, to use the words of Mr. Sully, "supplemented by an accompaniment or escort of revived sensations, the whole aggregate of actual and revived sensations being solidified or integrated into the form of a _percept_; that is, an apparently immediate apprehension or cognition of an object now present in a particular locality or region of space."[FV] Throughout the whole process of the formation of constructs by immediate association, and their definition by examination, we were dealing with perception and percepts. But when we reach the stage when particular qualities were isolated, then we enter the field of _conception_. The isolates are _concepts_. Class-names, reached through processes involving isolation, stand for concepts. And completed constructions, involving synthesis of the results of analysis, contain conceptual elements. The word "concept," however, is used in different senses by different authors. Mr. Sully says,[FW] for example, "A concept, otherwise called a general notion, or a general idea, is the representation in our minds answering to a general name, such as 'soldier,' 'man,' 'animal.'... Thus the concept 'soldier' is connected in my mind with the representations of various individual soldiers known to me. When I use the word 'soldier,' ... what is in my mind is a kind of composite image formed by the fusion or coalescence of many images of single objects, in which individual differences are blurred, and only the common features stand out distinctly.... This may be called a typical or generic image." But Noiré, quoted by Professor Max Müller,[FX] taking another illustration, says, "All trees hitherto seen by me leave in my imagination a mixed image, a kind of ideal presentation of a tree. Quite different from this is my concept, which is never an image." I follow Noiré; and I hold that the image, in so far as it is an image, whether simple or composite,[FY]