To properly grasp a concept (beyond a certain level of abstraction), it needs to be defined. “Table” is pretty clear by looking; “republic” is not. To properly define a concept, one needs to (1) follow the nature of reasoning and logic in (2) identifying facts and aspects of the real world. That is, one needs to recognize that a definition has specific characteristics, that there are rules or norms of proper definition. (You don’t get a proper definition from most dictionaries; they give usage.)
For the SAT takers or takers-to-be out there: using the rules of definition to properly define a concept — even trying to use the rules to properly define a concept — will help you better retain and assimilate your SAT words. You’ll be better able to use the words in the vocabulary (fill-in-the-blank) section, you’ll be better able to make sense of the words when you read them, and you’ll be better able to use those words to enrich your essays.
In fact, some essays call for a definition of terms. And, remember, the SAT and ACT essays are scored primarily on “critical thinking” skills. Give good definitions and give a good, logical defense of your definitions, and you’ll get “bonus points.” Some essays can even be structured around developing a definition of a term!
So now what are the rules, or norms, of proper definition?
What good fortune to have H.W.B. Joseph’s An Introduction to Logic (Clarendon Press, 1906) available online at Questia in their Free Books section to help us! You can also download Joseph’s Logic from Google Books, or you can read and download the Logic from the Internet Archive. Joseph does a masterful job of discussing the nature of definition and the rules of proper definition.
Joseph says (Chapter V: The Rules of Definition and Division, pp. 97-101):
The rules of definition are as follows: 1. A definition must be commensurate with that which is to be defined i.e., applicable to everything included in the species defined, and nothing else. 2. A definition must give the essence of that which is to be defined. The essence of anything is that in virtue of which it is such a thing. It is in virtue of being a three-sided rectilinear figure that anything is a triangle: in virtue of being an institution for the education of the young, that any place is a school: in virtue of having value in exchange, that anything is wealth. … 3. A definition must be [by genus and differentia]. The better the definition, the more completely will the differentia be something that can only be conceived as the modification of the genus: and the less appropriately therefore will it be called a mere attribute of the subject defined. Thus a lintel is a piece of timber forming the top of a doorway; it can hardly be called an attribute of a lintel that it forms the top of a doorway, for that implies that having already the concept of a lintel, I notice this further as a characteristic of it; whereas really, until I have taken this into account, I have no concept of a lintel. On the other hand, if sodium be defined as an element exhibiting line D in the spectrum, the differentia here may fairly be called an attribute. For one may have a pretty definite notion of sodium without knowing that it exhibits this line in the spectrum. … 4. A definition must not be in negative where it can be in positive terms. The propriety of this rule is obvious. A definition should tell us what the thing defined is, not what it is not. A scalene triangle, for example, should be defined, not as one containing neither a right angle nor an obtuse angle, but as one containing three acute angles. In this case it is true that a very little knowledge of geometry would enable any one to extract from the negative information of the former definition the positive characterization of the latter. But a negative definition is in itself inadequate, and it would in most cases leave us quite uncertain what the subject positively is. If real property were defined as property that cannot be transferred from place to place, we should not necessarily realize that it was property in land. If anger be defined as an impulse not directed to obtaining for oneself a pleasure, who is to understand that it is an impulse to repay an imagined hurt? A definition in negative terms is, with one exception, always faulty; its futility depends on the precision of the positive meaning which the negative terms may happen to convey. The one exception to the faultiness of a definition in negative terms is furnished by concepts that are themselves privative or negative. A bachelor is an unmarried man; and the very meaning of the term is to deny the married state. Injustice, said Hobbes, is the not keeping of covenant. A stool is a seat for one without a back to it. But it must not be assumed that because a term is negative in form it need be negatively defined; intemperance is the excessive indulgence in strong drink. 5. A definition must not, directly or indirectly, [define] the thing by itself. A thing is defined by itself directly, if the term itself or some synonym of it enters into the definition. The sun might, for example, be thus defined as a star emitting sunlight; or a bishop as a member of the episcopate. Such error is a little gross; but in the indirect form it is not uncommon. It arises with correlative terms, and with counter-alternative where one is used to define the other. A cause, for example, is ill defined as that which produces an effect, or an effect as the product of a cause; for correlatives must be defined together, and it is the relation between them that really needs to be defined; this is the ground of applying both the correlative terms, and in defining this, we define them. The objection to defining a term by help of its counter-alternative is that the latter may with equal right be defined by it. If an odd number is a number one more than an even number, the even is similarly that which is one more than the odd. … 6. A definition should not be expressed in obscure or figurative language. The use of obscure words where plain and familiar words are available is a fault in definition, because it militates against the object of definition – viz. that one may understand the nature of the thing defined. The use of figurative, or metaphorical, language is a graver fault, because metaphors, where they are intended to do more than merely to embellish speech, may suggest or lead up to a right understanding of a subject, but do not directly express it. Memory, for example, is ill defined as the tablet of the mind; for though knowledge is preserved in memory, so that we can recover it again, and writing is preserved in tablets for future reference, yet the two things are very different, and the actual nature of what we call memory is as little like a tablet as possible. …Now it’s your turn: try the rules out!! Study, and try again!! Defining terms takes work and is not a skill we learn overnight. You should give yourself slow years to learn, practice and master this skill; you should not try to force and cram it. After all, you get an education over the course of ten to twelve years; you don’t get an education in two months…or less. Again, it takes years to become a proficient athlete, dancer, musician, or horseback rider; you don’t become proficient in a week. Good definitions come from immersing oneself in the concretes and context of a concept, which takes time, effort, and patience. And the work is worth it: Just as strength and fluency of body is a joy, so also is strength and fluency of mind. As Aristotle said in his Rhetoric: “It is absurd to hold that a man ought to be ashamed of being unable to defend himself with his limbs, but not of being unable to defend himself with speech and reason, when the use of rational speech is more distinctive of a human being than the use of his limbs.” BTW, if you would like to purchase a copy of Joseph’s Logic, you may do so at such places as the Paper Tiger or Abebooks.com.