A species is a class of things the name of which recalls more particulars than the name of another class or genus with which it is compared. Bird is a species when compared with the class animal.

In examining language, it will be found that the larger portion of words in common use are names of genera and species—that is, they are words employed to recall ideas as they are arranged in genera and species. It is only those words that are proper names which recall conceptions of the particular existences by which we are surrounded. Some of these surrounding existences are furnished with these particular names, and others can be designated and distinguished from each other only by a description. Thus we see some hills around our horizon, some of which have a peculiar name, and others can be designated only by describing the circumstances which distinguish them from all other hills.

A definition of a word is an enumeration of the several qualities or circumstances which distinguish certain things from all others, and which are recalled to the mind when the word is used. Thus, if the word animal is to be defined, we do it by mentioning the circumstances of its existence and animal life, as the ideas recalled by the word. Generally, a word is defined by mentioning the name of some genus of which the thing intended is a species, and then adding those particular qualities which the species has, in addition to those included under the genus. Thus, if we are to define the word man, we mention the genus animal, and then the qualities which man has in addition to those possessed by other animals. Thus: "Man is an animal, having the human form, and a spirit endowed with intellect, susceptibility, and will."

There are some words which recall only one quality or circumstance, and which, therefore, can not be defined like the words which recall various qualities and circumstances, as joy, sorrow, color, and the like. Such words as these are defined by mentioning the times or circumstances when the mind is conscious of the existence of the idea to be recalled by the word. Thus joy is "a state of mind which exists when any ardent desire is gratified." Color is "a quality of objects which is perceived when light enters the eye."

Those conceptions which can be defined by enumerating the several qualities and circumstances which compose them are called complex ideas, and the words used to designate them are called complex terms. Such words as landscape, wrestler, giant, and philosopher, are complex terms. The word landscape recalls a complex idea of various material things. The word wrestler recalls an idea of a material object and one of its actions. The word giant recalls an idea of a thing and its relation as to size. The word philosopher recalls the idea of a thing and one of its qualities.

Those conceptions which are not composed of several qualities and circumstances, but are themselves a single quality or circumstance, are called simple ideas, and the words used to recall them are called simple terms. Such words as sweetness, loudness, depth, pain, and joy, are simple terms. Some terms which express emotions of the mind are entirely simple, such as sorrow, joy, and happiness. Others are words which recall an idea of a simple emotion and of its cause, such, for example, as gratitude, which expresses the idea of an emotion of mind and also that it was caused by some benefit conferred. Words that express simple ideas can be defined only by some description of the circumstances in which these ideas exist, or by a reference to their causes or effects.

CHAPTER XII.
ASSOCIATION.

The causes of the particular succession of our ideas, and the control which the mind has in regulating this succession, is a subject no less interesting than important; for if by any act of choice the mind has the power of regulating its own thoughts and feelings, then man is a free agent and an accountable being; but if the conceptions and the emotions depend entirely upon the constitution of things, and thus, either directly or indirectly, on the will of the Creator, then man can not be accountable for that over which he can have no control.

In the preceding chapter has been illustrated the effect which the co-existence of desire has in regard both to our sensations and our conceptions, tending to make those which are fitted to accomplish the object desired very vivid and prominent, while others, to a greater or less extent, disappear.