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Abstraction. All our notions, or Understanding-conceptions, are, as we have seen, complex, constituted of elements furnished by the primary faculties, Sense, Consciousness, and Reason. To make an abstraction of a notion is, in thought, on the ground of the ideas of resemblance and difference, to separate these elements from one another, giving special attention to some one, or more, or each of them in particular. Into our conceptions of body, for example, the elements of form, solidity, color, &c., enter. Now in the light of the ideas of resemblance and difference, the Intelligence perceives at once, that the element of solidity differs from that of form, and that of color from either of the others. In thought, therefore, either of these elements may be so separated from all of the rest, that it shall be the object of special observation. Thus our conceptions of each element of the object, and consequently our notions of the entire object, may become more or less distinct and complete.

Abstract Notions, what, and how formed ? When the Intelligence, in the sense above explained, makes abstraction of a particular element of an object or conception, it may, ever after, conceive and speak of that element without reference to the particular object from which it was abstracted. Then we have what is denominated an abstract notion, such as is designated by the terms redness, sweetness, hardness, &c.

General Notions, how formed. Originally all Understanding-conceptions are particular.

From these, all notions, abstract and general, are formed. How is the general evolved from the particular? Let us suppose that, in conformity to the process above described, the Intellect has formed notions of two particular objects, mountains, for example. These two notions lie together under the eye of Consciousness. In the light of the idea of resemblance and difference, the mind at once perceives that there are certain elements common to the two. Abstraction is made of these elements, and a third notion is formed, embracing them alone. Here is the first appearance of a general notion. When a third mountain is perceived, and a notion formed of that, the general notion undergoes a new modification, and now embraces those elements only common to the three. Thus the process of abstraction goes on, till the general notion pertains to those elements only common to all mountains. This same process takes place in all instances in which general notions are evolved from particular ones.

CLASSIFICATION. The process of classification can now be readily explained. We will refer back to the case when two particular notions were in the mind, and the general was evolved from them. As soon as the notion last named appears, the two particulars are subsumed or classed under it. In the same manner every particular previously perceived is arranged under the general, in all the successive modifications which it subsequently undergoes.

Forms of Classification. There are three distinct points of view from which objects are classified.

1. In view of general resemblances, they are classed, on the ground of common qualities, under general notions, such as man, animals, &c.

2. In view of some one quality without reference to resemblance in any other particular, they are classed under notions purely abstract, such as redness, whiteness, &c. We often class objects together, as white, hard, sweet, &c., without reference to their relations, in any other particulars.

3. Objects are classed together, in view of their correspondence to pure rational conceptions, such as a circle, square, right and wrong, &c.

Classification, in what sense arbitrary. It will readily be seen that classification from one point of view, will run directly across and back of that which is formed from another. How distinct and opposite, for example, will classification be which is founded in view of some one abstract quality, such as redness, from that which is based upon general resemblance, and formed under a general conception. Equally distinct and unlike either of the others will be the arrangement of objects, which are classed together under some pure rational conception.

For these reasons classification has, by many been regarded as perfectly arbitrary. It is true, that we are at liberty to adopt either of the principles of classification above described we please. In this respect, the process is perfectly arbitrary. If we classify at all, however, we must adopt one or the other of the forms under consideration, no other forms being conceivable. When we have selected our principle also, the subsequent arrangement of objects in conformity to it is necessary. In very important respects, therefore, classification has its laws, which are by no means arbitrary.

Genera and Species. In the process of classification, objects are ranged together as genera and species. Thus we have the genus tree, and the different classes, or species of fruit-bearing and forest trees, ranged under it. A species also is often itself a genus relatively to particular and distinct classes belonging to that species. If fruit-bearing be assumed as the genus, then we have the apple, plum, peach, cherry trees, &c., ranged as species under this generic term. The illustration might be extended indefinitely, from the highest to the lowest forms of genus and species. Our present concern is with the principle on which objects are thus classed. It is that to which we have frequently referred in this Chapter, the idea of resemblance and difference. The genus is formed on the perception of remote resemblances. Species under the genus are formed on the perception of important differences; while objects are classed under the species, on the perception of resemblances more near and special. Thus the genus tree is formed on the perception of qualities common to all trees. The species fruit-bearing and forest trees, are separated from each other, on the perception of important differences, each

species being formed on the ground of resemblances more near and particular than those designated by the general term tree.

In illustration of the process in which classes, as genus and species, are formed, we will take the case of the child. A certain object stands near the paternal mansion, which he has learned to designate by the term tree. By and by he sees another object resembling this in all important particulars. Here, he says, is another tree. In his mind they are distinguished as greater and less, and in respect of location. Here is the obscure development of the ideas of genus and species. At length, however, he perceives a tree differing in very important particulars from either of the others. He now asks the question, what kind of tree is this? The answer is, we will suppose, a maple tree. Then the inquiry arises, what tree is that which stands near the house? He is told that it is an elm tree. He has now the idea of the genus tree, formed on the perception of common qualities, and of two species, separated from each other on the perception of important differences. All trees subsequently perceived, presenting similar resemblances and differences, will be separated and arranged accordingly. As other trees, differing from either of these, are perceived, they will be separated and classed in a similar manner. Throughout the whole process, one idea guides the mind, that of resemblance and difference.

GENERALIZATION. But few words are requisite in the explanation of the mental process called Generalization. A general fact is a quality common to every individual of a given class. It may be peculiar to that class ; or, while it belongs to each individual of the class, it may appertain to individuals of other classes.

Rules in respect to Generalization. 1. No fact must be assumed as general, which does not belong to each individual of the class to which it is referred.

2. No general fact must be assumed as peculiar to one class, which, though strictly general in respect to that class, nevertheless appertains to individuals of other classes.

3. No fact must be assumed as general without a sufficient induction of particulars, to remove all doubt in respect to the question whether it is, or is not, a general fact,

The Term General sometimes used in a limited sense. In common usage, a fact is called general, when it belongs to a majority of the individuals of a certain class. In such a case, its existence in connection with an individual of the class is only probable. Great injury is often done to individuals in the application of facts of this kind.

GENERAL TERMS. In the progressive developments of mental science, the question has long been agitated among philosophers, whether when we use general terms, such as man, animal, there are ideas in the mind, and objects in the universe around us, corresponding to these terms, or whether they are mere terms, without corresponding ideas and objects. In respect to such terms, three distinct theories have been formed by as many different sects of philosophers.

Theory of the Realists. The first was maintained by a particular class of the schoolmen, and deduced from certain principles, real or supposed, maintained by Aristotle. The theory was this : There exists in nature, not only individual substances, but certain essences, corresponding with the general ideas which exist in the mind. When, for example, we use the term man, it was maintained that there exists in the world around us a certain essence, which is found in no individual of the species, and which exists in connection with no individual, but which corresponds with the idea in the mind, which idea is designated by the above term. So of every other general term. The sect of philosophers maintaining this theory was called Realists. Their dogmas have been long since exploded.

Theory of the Nominalists. Another theory directly opposed to the above, was maintained by a sect of philosophers which arose in the eleventh century. “According to those philosophers,” says Mr. Stewart, “ there are no existences in nature, corresponding to genral terms; and the objects of our attention, in all speculations, are not ideas, but words.” This sect was called the Nominalists. As there are no existences in nature, according to this sect, corresponding with general terms, all our specula

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