Classes of Concepts.
In the preceding chapter we have seen the process of conception--of the forming of concepts. _The idea of a general class of things or qualities is a concept._ Each concept contains the qualities which are _common to all_ the individuals composing the class, but not those qualities which pertain only to the minor classes or the individuals. For instance, the concept of "bird" will necessarily include the common qualities of warm-bloodedness, featheredness, wingedness, oviparousness, and vertebratedness. But it will _not_ include color, special shape, size, or special features or characteristics of the subfamilies or individuals composing the great class. The class comprises the individuals and subclasses composing it; the concept includes the general and common qualities which _all_ in the class possess. A _percept_ is the mental image of a particular thing; a _concept_ is the mental idea of the general qualities of a class of things. A percept arises from the perception of a sensation; a concept is a purely mental, abstract creation, whose only existence is in the world of ideas and which has no corresponding individual object in the world of sense.
There are two general classes of concepts, namely: (1) concrete concepts, in which the common qualities of a class of things are combined into one conceptual idea, such as "bird," of which we have spoken; (2) abstract concepts, in which is combined the idea of some _quality_ common to a number of things, such as "sweetness" or "redness." Jevons's well-known rule for terms is an aid in remembering this classification: "_A concrete term is the name of a thing; an abstract term is the name of a quality of a thing._"
It is a peculiar fact and rule of concrete concepts that (1) the larger the class of things embraced in a concept, the smaller are its general qualities; and (2) the larger the number of general qualities included in a concept, the smaller the number of individuals embraced by it. For instance, the term "bird" embraces a great number of individuals--all the birds that are in existence, in fact, but it has but few general qualities, as we have seen. On the contrary, the concept "stork" has a much larger number of general qualities, but embraces far fewer individuals. Finally, the individual is reached, and we find that it has more qualities than any class can have; but it is composed of the smallest possible number of individuals, one. The secret is this: No two individuals can have as many qualities _in common_ as each has individually, unless they are precisely alike, which is impossible in nature.
IMPERFECT CONCEPTS.
It is said that outside of strictly scientific definitions very few persons agree in their concepts of the same thing. Each has his or her own concept of the particular thing which he or she expresses by the same term. A number of persons asked to define a common term like "love," "religion," "faith," "belief," etc., will give such a variety of answers as to cause wonderment. As Green says: "My idea or image is mine alone--the reward of careless observation if imperfect; of attentive, careful, and varied observation if correct. Between mine and yours a great gulf is fixed. No man can pass from mine to yours, or from yours to mine. Neither in any proper sense of the term can mine be conveyed to you. Words do not convey thoughts; they are not vehicles of thoughts in any true sense of that term. A word is simply a common symbol which each associates with his own idea or image."
The reason of the difference in the concepts of several persons is that very few of our concepts are nearly perfect; the majority of them are quite imperfect and incomplete. Jevons gives us an idea of this in his remarks on classification: "Things may seem to be very much like each other which are not so. Whales, porpoises, seals, and several other animals live in the sea exactly like a fish; they have a similar shape and are usually classed among fish. People are said to go whale fishing. Yet these animals are not really fish at all, but are much more like dogs and horses and other quadrupeds than they are like fish. They cannot live entirely under water and breathe the air contained in the water like fish, but they have to come to the surface at intervals to take breath. Similarly, we must not class bats with birds because they fly about, although they have what would be called wings; these wings are not like those of birds, and, in truth, bats are much more like rats and mice than they are like birds. Botanists used at one time to classify plants according to their size, as trees, shrubs, or herbs, but we now know that a great tree is often more similar in character to a tiny herb than it is to other great trees. A daisy has little resemblance to a great Scotch thistle; yet the botanist regards them as very similar. The lofty growing bamboo is a kind of grass, and the sugar cane also belongs to the same class with wheat and oats."
It is a matter of importance that clear concepts should be formed regarding at least the familiar things of life. The list of clear concepts should be added to from time to time by study, investigation, and examination. The dictionary should be consulted frequently, and a term studied until one has a clear meaning of the concept the term seeks to express. A good encyclopedia (not necessarily an expensive one, in these days of cheap editions) will also prove very useful in this respect. As Halleck says: "It must be borne in mind that most of our concepts are subject to change during our entire life; that at first they are made only in a tentative way; that experience may show us, at any time, that they have been erroneously formed, that we have abstracted too little or too much, made the class too wide or too narrow, or that here a quality must be added or there one taken away."
It is a good practice to make a memorandum of anything of which you may hear, but of which you know nothing, and then later to make a brief but thorough investigation of that thing, by means of the dictionary and encyclopedia, and of whatever good works may be obtained on the subject, not leaving it until you feel that you have obtained at least a _clear idea_ of what the thing really _means_. A half hour each evening devoted to exercise of this kind will result in a wonderful increase of general information. We have heard of a man who made a practice of reading a short article in the encyclopedia every evening, giving preference to subjects generally classed as familiar. In a year he made a noticeable advance in general knowledge as well as habits of thought. In five years he was looked upon by his associates as a man of a remarkably large field of general information and of more than ordinary intelligence, which verdict was a just one. As a rule we waste far more time on worthless fiction than we are willing to devote to a little self-improvement of this kind. We shrink at the idea of a general course of instructive reading, little realizing that we can take our study in small installments and at a very little cost in time or labor.
Our concepts form the material which our intellect uses in its reasoning processes. No matter how good a reasoner one may be, unless he has a good supply of general information about the things of which he is reasoning, he will not make much real headway. We must begin at the bottom and build a firm foundation upon which the intellectual structure may be erected. This foundation is composed of _facts_. These facts are represented by our clear and correct concepts.