As you begin to work on your essay, some of the following might help you avoid various confusions, but I certainly do not expect you to incorporate any of the following into your essay.
Definitions are about Words. A definition is a sentence that expresses the meaning of a word. (The previous sentence is a definition of ‘definition’.) This is a common point of confusion, as many people often think that definitions are about things, when in fact they are about words (terms). We can define ‘dog’ but not dogs, and certainly not some particular dog. Similarly, we can define ‘dog’ but not ‘Fido’ (i.e., the name of a particular dog).
There are many kinds of definitions, and these can be sorted either by their purpose (i.e., what we want the definition to do for us) or by the technique used in constructing the definition, and this construction is best understood in terms of two different kinds of meaning, which we will turn to next.
The Meanings of Words. Most words have two kinds of meanings: intensional and extensional. Intensional meaning consists of the qualities or attributes that the word brings to mind (the connotation of the word), while extensional meaning consists of all the things that are named by that word (the denotation of the word). For instance, ‘dog’ connotes furry, four legs, generally friendly towards humans, a wagging tail, while it denotes the group of all actual dogs. These two kinds of meaning are important for distinguishing the different definitional techniques.
Definitional Techniques.
— There are three standard ways of defining words in terms of their extensional or denotative meaning.
Demonstrative definitions capture the meaning of a word by pointing to a particular member of the group (e.g., defining ‘blue spruce’ by pointing at a blue spruce, and perhaps also saying “That is a blue spruce”).
Definitions by subclass will name various subclasses of individuals denoted by the word (e.g., defining ‘cetacean’ by saying “A cetacean is either a whale, a dolphin, or a porpoise”).
Definitions by enumeration define their term simply by naming individuals within the class (e.g., defining ‘genius’ by saying “A genius is someone like Albert Einstein, Johann Sebastian Bach, or Alan Turing”).
— There are four standard ways of defining words in terms of their intensional or connotative meaning:
Definitions by synonym hope to capture the meaning of a word by offering a close (and hopefully better known) synonym (e.g., ‘despicable’ means hateful)
Etymological definitions offer an account of the origin of a word (e.g., ‘despicable’ comes from the Latin word that means “to look down on”).
Operational definitions anchor the meaning in some physical test or procedure (e.g., a solution is acidic if litmus paper turns pink when dipped into it, or a subject has brain activity when an electroencephalograph shows oscillations when attached to the subject’s head).
Definitions by genus and difference locate the meaning of the word within a larger group (the genus), indicating what distinguishes (the difference) this kind of thing from the rest of the group (e.g, ‘robot’ means a machine that can move autonomously). You will find this last technique the most commonly used, as it can be used to create each of the following kinds of definitions.
Definitions Sorted by their Purpose. We have developed different kinds of definitions to fulfill different purposes. The following are the most common.
Lexical definitions give an account of how a word is actually used in a population (this is the kind of definition normally found in dictionaries).
Stipulative definitions are created to assign a meaning to a newly-coined word, or to mark a novel use of a word (e.g., the relatively recent interbreeding of tigers and lions in captivity have resulted in the words ‘tigon’ and ‘liger’ along with their stipulative definitions).
Precising definitions are given to a common word whose meaning is vague, and where a more precise meaning is needed for a particular purpose. For instance, the lexical definition of ‘poor’ is something like “lacking sufficent money to live at a normal level in a particular society,” but for purposes of an economic report it might need to be tightened up, such as “a single person under 65 years earning less than $8,959 per year” (this was the definition of ‘poor’ used in 2000 by the U.S. Census Bureau).
Theoretical definitions are used for words that belong to a system of ideas where the meaning of each word is closely related to the larger system and the meanings of the other words. These theoretical definitions are tied to a specific way of understanding a thing (and the larger world of which it is a part). For instance, a standard lexical definition of ‘heat’ is “the quality of being hot,” and this meaning often serves our purposes. But in physics, ‘heat’ is better understood as “a form of energy arising from the random motion of the molecules of bodies,” and this meaning situates the words into a larger framework by which we gain a much clearer theoretical understanding of what heat is.