The trouble does not end here. Concepts not only include the general idea of _things_, but also the general idea of the _qualities of things_. Thus sweetness, hardness, courage, and energy are concepts, but we cannot form a mental image of them by themselves. We may picture a sweet _thing_, but not sweetness itself. So you see that a concept is a purely abstract mental idea--a symbol--akin to the figures 1, 2, 3, etc., and used in the same way. They _stand_ for general classes of things. A "term" is the verbal and written expression of the general idea or concept. The student is requested to fix these distinctions in his mind, so as to render further understanding of them easy. CHAPTER XXI. Conception. The process of conception has been well defined by Gordy as "that act of mind by which it forms an idea of a class; or that act of the mind that enables us to use general names intelligently." He adds: "It is, of course, understood that I am using the word 'class' to denote an indefinite number of individuals that resemble each other in certain particulars." PERCEPTION. The first step in conception, as we have seen, is that of perception. It is readily perceived that the character of our intellectual processes depends materially upon the variety, clearness, and accuracy of our perceptions. Therefore, again, we would refer our students to the chapter in which we have stated the importance of clear perception. MEMORY. The future steps of conception depend materially upon the clearness of the memory, as we can classify objects only by remembering their qualities beyond the immediate moment of actual, original perception. Therefore, the memory should be strengthened for this as well as other objects. ABSTRACTION. The second step in conception is that of the mental abstraction of qualities from the observed thing. That is, we must perceive and then mentally _set aside_ the observed qualities of the thing. For instance, man first perceived the existence of certain qualities in things. He found that a certain number of things possessed some of these qualities in common, while others possessed other qualities in the same way, and thus arose classification from comparison. But both comparison and classification are possible only by abstraction, or _the perception of the quality as a "thing"_; thus, the abstraction of the idea of the quality of _sweetness_ from the idea of sugar. Sweetness is a _quality_ rather than a thing itself. It is something possessed by sugar which helps to make sugar what it is.