Definition

Chapter III — The Idea Explained

This Chapter sets forth the method of explaining ideas. Ideas, as we have seen, may be obscure or vague, and explanation is needed to render them clear and distinct. Such explanation is required not only for the proper conveying of ideas to others, but also for the clarifying of ideas in our own minds.

Now ideas are explained by analyzing them and setting forth the results of the analysis. We may analyze the Comprehension of an idea and show the essential notes that make it up; and we express the results of such analysis in an essential Definition. And we may analyze the Extension of an idea and group its inferiors into classes convenient for the purpose we have in hand; and such grouping or classification is called Logical Division. That Definition and Logical Division may serve their purpose of clarifying ideas and rendering them distinct and complete, it is necessary that these explanations be developed according to well defined laws or rules. This Chapter therefore discusses the matters of Definition and Logical Division and the rules by which these are rendered serviceable in the work of explaining ideas.

The Chapter is accordingly divided into two Articles, as follows:

• Article 1. Definition
• Article 2. Logical Division

Article 1. Definition

a) Doctrine of Definition    b) Rules of Definition

a) Doctrine of Definition

In the widest sense, definition is the explanation of an idea or term according to its content or use. Varieties of definition may be set forth, beginning with this general description, and thus we may arrive at a precise knowledge of the nature of real essential definition with which alone Dialectics is concerned. We distinguish the following types of definition:

i. Nominal Definition. Nominal definition explains a term by telling something about it considered as a name. Nominal definition may be constructed:

1. according to etymology, as, ” ‘Hippopotamus’ is derived from two Greek words, hippos (horse) and potamos (river)”;
2. by translation, as, ” ‘Hippopotamus’ means ‘river horse’ ”;
3. by substitution, as, “Theodicy is Natural Theology.”

ii. Real Definition. Real definition tells the content of an idea with more or less completeness and accuracy. It tells something about the thing for which the idea (and term) stands. It is:

i. Essential, when it declares exactly what the essence of a thing is. Essential definition is either physical or metaphysical according as it expresses the essential objective elements that make up a reality, or the essential notes that make up an idea in the mind. Thus, “Man is a creature made of body and soul” is a physical definition; while “Man is a rational animal” is a metaphysical definition. In simpler language, a physical definition explains an essence by naming its parts; while a metaphysical definition explains an idea by naming its essential notes.

ii. Descriptive definition (or simply Description), when it tells something about an essence in itself, or its properties or accidents, but does not adequately express what that essence is. Description may be accidental, as, “Man is a biped without feathers”; it may be proper or attributive, as, “Man is a walking and talking being”; it may be genetic (showing origins), as, “Man is formed of the slime of the earth”; it may be causal, as “Man is made by God (efficient cause) to know and love God (final cause).”

Dialectics, as we have remarked, has to do only with real essential definition.

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b) Rules of Definition

The following rules are most important. Remember that Dialectics is the science of correct thinking. Now no one can think correctly — in matters intricate and involved — without a clear grasp of the elements of thought (ideas), and such clear knowledge depends largely upon adequate essential definition. Thus one must know what a definition is and should be. The test of definition, as well as the manner of constructing it, is contained in the following set of four rules.

Rule I. The definition must be exact.

The rule means that the definition must square precisely with the idea (term) defined, not falling short or extending beyond the limits of the latter. Another way of expressing this rule is: Let the definition be neither wider nor narrower than the term defined. The following definitions offend against this rule:

• Cats are domestic animals;
• Charity is that which covers a multitude of sins;
• Man is an animal;
• A circle is a plane figure.

Rule II. The definition must be clear.

The purpose of definition is to clarify ideas. That purpose is defeated if the definition be as obscure as what it should clarify. This rule is violated by the use of ambiguous, metaphorical, or indefinite terminology, and sometimes by the use of complex technical expressions. The following definitions violate this rule:

• A window is an orifice in an edifice for the exclusion of elemental disturbances, and the admission of illumination through translucent substances;
• Evolution is the transit from the homogeneous to the heterogeneous;
• A biological species is a class marked by morphological discontinuity and interspecific sterility.

Rule III. The definition must not contain the term defined, even implicitly.

The definition is meant to clarify, but we do not clarify or explain a thing by repeating its name. I do not clarify the idea of circle by defining it as “a circular line.” The following violate this rule:

• A metal is a metallic substance;
• A body is any substance of bodily character;
• Psychology is the scientific study of psychic activities;
• “The duties of an archdeacon are purely archidiaconal.”

Rule IV. Essential definition consists of proximate genus and specific difference.

The Proximate Genus sums up all the essential notes that enter into the Comprehension of an idea save the last. And the Specific Difference gives this ultimate note. Hence Proximate Genus plus Specific Difference equals the sum of essential notes — the entire essence. The student is referred to the study of The Porphyrian Tree, page 34. Definitions that violate this rule are exampled above in the paragraph on Description.

The following jingle, wretched as doggerel may be, is yet a valuable mnemonic, and sums up the Four Rules of Definition in proper order:

Defining, be exact and clear;
Don’t let the term defined come near;
Essential Definition mocks
All but Spec. Diff. and Genus Prox.

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Summary of the Article

In this Article we have learned what is meant by nominal definition, which is only the explanation of the sense of a term. We have also learned what real definition is, and this we have subdistinguished as essential definition and description. We have studied and exemplified the Four Rules of Definition.