From the above we may see the fundamental differences between a Percept and a Concept. The Percept is the mental image of a real object–a particular thing. The Concept is merely a _general idea_, or general notion, of the common attributes of a class of objects or things. A Percept arises directly from sense-impressions, while a Concept is, in a sense, a pure thought–an abstract thing–a mental creation–an ideal.
A Concrete Concept is a concept embodying the common qualities of a class of objects, as for instance, the concrete concept of _lion_, in which the general class qualities of all lions are embodied. An Abstract Concept is a concept embodying merely some one quality generally diffused, as for instance, the quality of _fierceness_ in the general class of lions. _Rose_ is a concrete concept; _red_, or _redness_, is an abstract concept. It will aid you in remembering this distinction to memorize Jevons’ rule: “_A Concrete Term is the name of a Thing_; _an Abstract Term is the name of a Quality of a Thing_.”
A Concrete Concept, including all the particular individuals of a class, must also contain all the common qualities of those individuals. Thus, such a concept is composed of the ideas of the particular individuals and of their common qualities, in combination and union. From this arises the distinctive terms known as the _content_, _extension_ and _intension_ of concepts, respectively.
The _content_ of a concept is _all that it includes–its full meaning_. The _extension_ of a concept depends upon its _quantity_ aspect–it is its property of including numbers of individual objects within its content. The _intension_ of a concept depends upon its _quality_ aspect–it is its property of including class or common qualities, properties or attributes within its content.
Thus, the _extension_ of the concept _horse_ covers all individual horses; while its _intension_ includes all qualities, attributes, and properties common to all horses–class qualities possessed by all horses in common, and which qualities, etc., make the particular animals _horses_, as distinguished from other animals.
It follows that the larger the number of particular objects in a class, the smaller must be the number of general class qualities–qualities common to all in the class. And, that the larger the number of common class qualities, the smaller must be the number of individuals in the class. As the logicians express it, “the greater the extension, the less the intension; the greater the intension, the less the extension.” Thus, _animal_ is narrow in intension, but very broad in extension; for while there are many animals there are but very few qualities common to _all_ animals. And, _horse_ is narrower in extension, but broader in intension; for while there are comparatively few horses, the qualities common to all horses are greater.
The cultivation of the faculty of Generalization, or Conception, of course, depends largely upon _exercise_ and _material_, as does the cultivation of every mental faculty, as we have seen. But there are certain rules, methods and ideas which may be used to advantage in developing this faculty in the direction of clear and capable work. This faculty is developed by all of the general processes of thought, for it forms an important part of all thought. But the logical processes known as Analysis and Synthesis give to this faculty exercise and employment particularly adapted to its development and cultivation. Let us briefly consider these processes.
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_Logical Analysis_ is the process by which we examine and unfold the meaning of Terms. A Term, you remember, is the verbal expression of a Concept. In such analysis we endeavor to unfold and discover the _quality-aspect_ and the _quantity-aspect_ of the content of the concept. We seek, thereby, to discover the particular general idea expressed; the number of particular individuals included therein; and the properties of the class or generalization. Analysis depends upon division and separation. Development in the process of Logical Analysis tends toward clearness, distinctness, and exactness in thought and expression. Logical Analysis has two aspects or phases, as follows: (1) _Division_, or the separation of a concept according to its _extension_, as for instance the analysis of a genus into its various species; and (2) _Partition_, or the separation of a concept into its component qualities, properties and attributes, as for instance, the analysis of the concept _iron_ into its several qualities of color, weight, hardness, malleability, tenacity, utility, etc.
There are certain rules of Division which should be observed, the following being a simple statement of the same:
I. _The division should be governed by a uniform principle._ For instance it would be illogical to first divide men into Caucasians, Mongolians, etc., and then further sub-divide them into Christians, Pagans, etc., for the first division would be according to the principle of race, and the second according to the principle of religion. Observing the rule of the “uniform principle” we may divide men into races, and sub-races, and so on, without regard to religion; and we may likewise divide men according to their respective religions, and then into minor denominations and sects, without regard to race or nationality. The above rule is frequently violated by careless thinkers and speakers.