Definition

To begin an argument, it is often useful to first define terms. Unless both sides of a debate can agree on meanings, it is difficult to argue intelligibly.

Formal definitions

In a formal definition, the term to be defined is given, the class to which it belongs is identified, and how it is differentiated from that class is stated. For instance

Formal Definition

Term	Class	Differentiation
A cat	is a feline	that is a small, domesticated, pet.

This table illustrates the three parts of a formal definition: term, class, differentiation.

Defining by Synonym

Synonyms are words that have the same basic meaning. Care should be used, however, when using synonyms as a form of definition. Oftentimes two words that have the same basic direct meaning (denotation) may be differentiated by shades of meaning, as between love and compassion (Barnet and Bedau 53). Words, also, often have different emotional connections or connotations. For instance, the words rock and stone have the same denotative meaning, but have very different connotations. Most people would suggest rocks are larger, more jagged, and less valuable than stones, which are felt to be smaller, smoother, and more valuable.

Defining by Etymology

One way to define a word is to examine its origins. For instance, the word circumlocution comes from two Latin words that literally suggest walking around a place. A useful tool for studying the etymology of words is the Oxford English Dictionary (OED), which traces the derivation and history of words, and includes quotations of early uses of the word.

While the etymology of a word can shed light on its meaning, words often evolve and change meaning (Corbett 54). For instance, in Hamlet, Act I, scene 4, Hamlet is summoned by the ghost of his dead father. When his companions, in fear for his life, try to stop him from following the ghost, Hamlet threatens them, saying "By heaven, I'll make a ghost of him that lets me!" Here, the word let is used to mean to prevent. But our current usage of the word let gives it the complete opposite meaning, to allow. Again, the OED can help students understand the evolution in the meaning of words.

Defining by Comparison

Sometimes it is useful to employ techniques of extended definition to explain the meaning of a word. Comparison can be used, especially by comparing a less familiar word or concept to one more familiar. Two special types of comparison are the simile and the metaphor.

A simile is a figure of speech that suggests a similarity between two different things. Robert Burns famous line "My love is like a red, red rose" is an example of a simile. One danger of using similes is failure to clarify for readers exactly how the two things are being related.

A metaphor is a figure of speech that makes an association between two very different things that share a significant trait or quality. For instance, Christ, in attempting to explain to his disciples his relationship to them, said "I am the vine, ye are the branches" (KJV, John 15.5). One danger of using metaphors is falling into cliches or hackneyed comparisons.

An analogy is an extended metaphor. While a metaphor makes an association between two things that share a single significant trait or quality, an extended metaphor suggest more expansive similarities, involving several traits or qualities. Scientists often use analogies to help non-scientists understand things that cannot be seen, like the atom, to things that can be seen like the solar system. The primary danger in using analogies lies in extending the analogy to cover more points of comparison than is warranted.

Defining by Example

Sometimes a word can be defined by offering examples that are representative, or serve as a pattern, model, or prototype of the thing to be defined. For instance, in the following passage, Terrence McLaughlin defines dirt by giving several examples (note, also, the use of comparison)

Earth, in the garden, is a valuable support and nourishment for plants, and gardeners often run it through their fingers lovingly; earth on the carpet is dirt. A pile of dung, to the dung beetle, is food and shelter for a large family; a pile of dung, to the Public Health Inspector, is a Nuisance. Soup in a plate, before we eat it, is food; the traces that we leave on the plate imperceptibly become dirt. Lipstick on a girl's lips may make her boy-friend anxious to touch them with his own lips; lipstick on a cup will probably make him refuse to touch it. (McLaughlin 14)

One danger in using examples is that the examples may not be relevant; that is, there may be disagreement on how well the examples "fit" the term being defined. Another danger lies in the extent by which the example fits the term being defined, since the example may be "fuller" that is warranted (Barnet and Bedau 53).

Defining by Stipulation

Sometimes it is necessary to stipulate a definition in order to fix the meaning of a term. Such a stipulation should be logical and reasonable, and will usually involve sufficient and necessary conditions for establishing the meaning of the term.

However, since stipulated definitions are arbitrary, they should not be used to replace perfectly acceptable definitions unless a clear and rational argument can be made for the stipulated definition. Terms should also not be defined by stipulation using emotional arguments that depend on the positive or negative connotations of a word appealing to prejudice, propaganda, or other strong emotions. It is absolutely necessary that the writer provide an adequate rational argument for the stipulated definition (Barnet and Bedau 53-5).

Other Methods of Defining

Defining by negation: One approach to explaining the meaning of a term is by showing what it is not. Defining by negations serves to limit the meaning of a term, identifying restrictions and exclusions (Clark 298). Legal definitions often reflect such restrictions on the meaning of a term.

Defining by classification: In this approach a term is first related to a class of similar items, and then the term is distinguished from the other members of the class (Clark 298). For instance, some people might distinguish pornography from erotica within the class of graphically sexual material by defining pornography as sexually graphic material that objectifies or denigrates women while erotica celebrates masculine and feminine human sexuality.

Defining by function: Sometimes it is useful to define a term by explaining how it works (Clark 299). Processes, like evolution or nuclear reactions, may be more clearly defined by explaining their function.

Assumptions and Premises

Oftentimes arguments are based in part on beliefs without evidence. Sometimes these can be values that the writer assumes the reader holds in common with the writer. For instance, a writer persuading students to study may assume that students want to succeed and that success is defined as earning good grades. But if a student is in the class just to be near his girlfriend and doesn't care whether he fails, the writer's assumption is flawed (Barnet and Bedau 57).

Sometimes an assumption is stated as a premise. According to Yagelski, Miller, and Crouse-Powers, a good premise should be

1. general enough that an audience is likely to accept it, thus establishing a common ground between writer and audience.
2. specific enough to prepare the way for the argument that will follow.

(Yagelski, Miller, and Crouse-Powers 28)

Two premises joined to create an argument leading to a conclusion creates a syllogism.

Major Premise: All fathers are parents.
Minor Premise: John is a father.
Conclusion: Therefore, John is a parent.

If one of the premises is assumed or left unstated, the resulting argument is called an enthymeme.

Since Mabel is a mother, Mabel must also be a parent.

Deduction

Deduction is the process of leading from statement to statement following the logical consequences of each statement and its relation to succeeding statements. Deductive arguments typically depend on syllogisms and enthymemes.

In order for the conclusions reached by deduction to be sound,

1. all of the premises must be true
2. the argument must be valid

(Barnet and Bedau 59)

A premise is considered true if it conforms to reality. An argument is valid if the conclusion logically follows from the premises. For instance, the following syllogism is false:

Major Premise: All parents are fathers.
Minor Premise: Mary is a parent.
Conclusion: Therefore, Mary is a father.

The syllogism is false because the major premise is false. Not all parents are fathers.

The following syllogism is invalid:

Major Premise: All fathers are parents.
Minor Premise: Mary is a parent.
Conclusion: Therefore, Mary is a father.

The syllogism is invalid because the major premise does not logically support the conclusion. While all fathers are parents, not all parents are fathers.

Induction

Induction is the process of drawing conclusions by generalizing from specific observations to discover patterns. Induction is the foundation of the scientific method. In the scientific method, the scientist

• makes observations of phenomena, and
• based on these observations, formulates a hypothesis (statement of pattern),
• then determines conditions for testing the hypothesis
• in order to reach a conclusion based on observed evidence that substantiates or contradicts the hypothesis

The simplest way to falsify a generalization is to provide a counterexample, that is, an example that contradicts the generalization (Barnet and Bedau 63).

Evaluating Evidence in a Post-Truth World

The following TED Talk by Alex Edmans discusses how people tend to believe things that match what they already believe (confirmation bias) and offers three tools for finding and evaluating information. A healthy skepticism about claims results in careful evaluation of and investigation into evidence.