One of the most important tools in logical reasoning is a dictionary.  Correct reasoning requires that we use words properly – according to their meaning.  Failure to use words correctly often results in miscommunication, but it can also result in errors in reasoning.  One of the most common logical errors in debates over origins concerns the definition of a single word.  And the error can be resolved by understanding how definitions work and by consulting a dictionary.

The definition of a word is a statement or series of statements that explains the word’s meaning.  There are four types of legitimate definitions.  And there is a fifth type of “definition” that is fallacious because it does not truly describe a word’s meaning.  It is critical to understand not only the definition of the words used in any argument, but also to know which type of definition is in use.  All of the four legitimate types of definitions have one thing in common: they explain the meaning of a word.

The meaning of a word is determined by usage.  In whatever way people typically use a word – that is what the word means.  Meaning is therefore conventional; it is determined by agreement or consensus.  A given word means whatever the majority decides it means.  This is quite different from a scientific truth.  The majority of people may be wrong about a fact of nature.  But the majority cannot be wrong about the meaning of a word because the meaning is determined by the majority.  Of course, an individual may be wrong about the meaning of a word.  And that can lead to countless errors.

A word is a linguistic token; it is a written or spoken symbol that represents something else.  The idea or object it represents is called the referent.  Consider the word ‘horse.’  The linguistic token is the five-letter written or spoken word, and the referent is the actual animal.  When we want to refer to the linguistic token, it is customary to put the word in single quotation marks, otherwise we naturally assume the referent is intended.  So ‘horse’ is a five-letter word, but a horse is an animal.

Note that there is no necessary connection between the token and the referent.  In other words, you cannot learn anything about an actual horse merely by studying the word ‘horse.’  A different language might use a very different word to describe the same animal, but the animal remains the same.  It is fallacious to draw any conclusion whatsoever about a referent merely on the basis of a linguistic token.  This confuses some people because a token may – in some cases – describe its referent.  For example, a bookmark is used to mark a page in a book, and a firetruck is a truck used to fight fires.

However, there is no logical requirement for a token to describe its referent, and hence, it is fallacious to conclude anything about a referent based on its linguistic token.  For example, a black hole is not a hole at all, Rhode Island is not actually an island, grapenuts are neither grapes nor nuts, and peanuts are neither peas nor are they actually nuts.  To conclude anything whatsoever about a referent on the basis of its token is therefore a logical fallacy – a mistake in reasoning.  It would be ridiculous to argue that Rhode Island doesn’t exist on the basis that it is not literally an island.  To avoid these kinds of errors in reasoning, we should review the four legitimate types of definitions, as well as the fifth fallacious “definition.”

Lexical Definition

A lexical definition is what we find in a dictionary or lexicon.  It reflects the range of meanings of any given word.  A dictionary is really a history book.  It records the recent history of the usage of words by the majority of people.  Most words have multiple lexical definitions.  The dictionary usually lists the most common usage first, with less common usages following.  Consider the word ‘plane.’  This can refer to a geometric surface in which any two points in that surface are connected by a straight line which is also in that surface.  Or a ‘plane’ can refer to any flat or level surface.  It can refer to an airplane.  It can refer to a tool used to shape wood.  ‘Plane’ can even refer to a type of tree.  And it also has a verb form with several definitions as well.

Since most words have multiple definitions, it is rather amazing that we can communicate at all.  How do we know which definition is in use?  There are two ways.  The first is context.  The surrounding words, sentences, paragraphs, and chapters all help to constrain the meaning.  When I say, “My flight was delayed because the plane required a minor repair”, context indicates that ‘plane’ refers to an airplane, not the geometric shape or any other meaning.

But sometimes, context isn’t enough.  In these cases, we must directly specify which definition we are using.  “By plane, I mean an airplane.”  That suffices to remove any ambiguity.

Failure to define terms and use them consistently is a leading cause of fallacious, muddled thinking and bad argumentation. 

One of the most common fallacies in debates on origins is the fallacy of equivocation.  This occurs when a person fails to define terms, and tacitly switches meanings within an argument.  Perhaps you have heard an argument like this: “Creationists reject evolution.  But evolution has been scientifically observed.  We have seen bacteria evolve resistance to antibiotics.  That’s evolution in action.  So, creationists are badly mistaken.”  This argument commits the equivocation fallacy because the word ‘evolution’ was not defined and was used in two different ways as if they were the same.

Namely, the evolutionist argues that evolution in the Darwinian sense of the descent of all life from a common ancestor must be true.  But the example he provides to demonstrate his claim is evolution in a different sense – the sense of a change within a kind.  It should be obvious that a change within a kind of organism does not remotely establish that all organisms have descended from a common ancestor.  But by referring to both as “evolution” the arguer hopes to get the person to accept one on the basis of the other.  This is also called a “bait and switch” fallacy.

Stipulative Definition

When scientists discover something new and unexpected, they often coin a new word or phrase to name the phenomenon.  Essentially, they are assigning a linguistic token to this newly discovered referent.  This is a stipulative definition.  Sometimes, a scientist may choose a token that is somewhat descriptive of the referent.  For example, physicists stipulated the term ‘tachyon’ which they define to mean “a particle that travels faster than light.”  ‘Tachyon’ is taken from the Greek word ‘takhus’ meaning “swift.”  It’s a fitting name.

On the other hand, when physicists stipulated terms for the six types of quarks, they named them “up, down, charmed, strange, bottom, and top.”  These terms have absolutely nothing to do with the properties of the quark in any way – and this is perfectly acceptable.  A biologist might discover a previously unknown organism, and name it in honor of his mentor.  The bottom line is that the word or words chosen for a stipulative definition are ultimately arbitrary.

So, when you stipulate a new definition, you are free to pick any token you wish, with one important constraint: it must be free of ambiguity.  Among other things, this means that you may not use a linguistic token that already has an established lexical definition.  So, if a biologist discovers some new reptile, he is not free to call it a dog.  The word ‘dog’ already has an established meaning.  The biologist could, however, name it a “scaly dog” because that phrase is not (yet) taken.

Interestingly, there is an exception to this exception.  You may stipulate a definition using a term that is already taken, if and only if context removes any ambiguity.  So, when computer developers invented a new type of computer interface, they were free to call it a ‘mouse.’  The word already had an assigned meaning, but in the context of computers it has a different meaning.  Most people would not be confused if someone said, “I need to purchase a new mouse for my computer.”  Context eliminates any ambiguity here.

In the same way that you are free to stipulate new definitions, other people are free to accept or reject your definition.  The biologist who discovers a new reptile and names it a “scaly dog” may find that other people don’t accept that term, and they eventually settle on something else.  Or perhaps they love the term and it catches on.  Stipulated definitions that catch on become lexical definitions over time.  As more people use the new term, its meaning becomes a consensus, and it is added to the dictionary.

As one example of this, older dictionaries will not contain the word ‘selfie.’  A few years ago, someone began using this new term to refer to an image of a person taken by the same person.  This was a stipulative definition at that time.  But now, it is a lexical definition since you can find it in any modern dictionary.  Essentially, all lexical definitions were once stipulative definitions – some were coined in the very distant past.  The original names of the animals were stipulated by Adam himself (Genesis 2:19-20).

Precising Definition

Extremely important in any technical field is the precising definition.  This is used to clarify a term that has some level of ambiguity.  A precising definition is based on a particular lexical definition, but adds an additional constraint for clarity in a specific context, one that is consistent with the lexical definition.

For example, suppose someone did a research project and concluded that wealthy Americans live several years longer on average than those of modest income.  For this report to be objective and useful, the researcher would have to specify quantitatively how he defines ‘wealthy.’  The dictionary doesn’t give a specific value.  The dictionary only defines ‘wealth’ as “a great quantity or store of money, valuable possessions, property, or other riches.”  But it does not specify precisely or quantitatively what constitutes “a great quantity.”  So, the researcher might state in the report, “By ‘wealthy’ I refer to those people with a gross annual income of at least $250,000.”

That would be a great precising definition for three reasons.  First, it is consistent with the dictionary definition.  We would have to agree that $250,000 per year constitutes “a great quantity” of money.  Second, it goes beyond the definition giving a precise cutoff for a term that is otherwise only qualitative: “$250,000” as opposed to “a great quantity.”  Third, it is for the specific context of the given study.  The researcher is not arguing that wealth in general must be defined by that specific number; rather, for the purposes of the particular research project, some value must be chosen.  Of course, a different researcher may have picked a different value for the cutoff.  And that would be perfectly fine too as long as he specified what the value is.

In a way, a precising definition is a combination of a lexical definition and a stipulative definition.  When using a precising definition, it must be consistent with the lexical definition of the term.  But we are free to stipulate additional constraints for a specific context, as long as we specify what those constraints are.  Those additional constraints must also comply with the lexical definition.  For example, the researcher should not state, “By wealthy, I mean anyone with an annual income of over $10” because no reasonable person would consider that “a great quantity.”

Theoretical Definition

A theoretical definition is a stipulative or lexical definition that is associated with a particular scientific theory.  For example, an orbital is defined as “a mathematically described region around a nucleus in an atom or molecule that may contain zero, one, or two electrons.”  You will find that definition in the Merriam-Webster dictionary, but you will also find it or a similar definition in certain science textbooks.  The definition is based on a particular scientific theory – the theory that atoms are composed of a central nucleus and one or more electrons surrounding that nucleus.  There is good evidence for this theory of course, but that is irrelevant to the definition.  The definition would remain the same even if the theory were discarded.

For example, luminiferous ether is defined as a “medium that in the wave theory of light permeates all space and transmits transverse waves.”  Scientists once believed that light required a material substance in which to travel, and that the substance filled all of space.  This was called luminiferous ether.   However, modern physicists largely reject this theory and would say that such ether does not exist.  The definition is still correct, however the theory turned out to be wrong.

Persuasive Definition

The above four definitions are rationally warranted and useful in logical reasoning.  However, there is a fifth type of “definition” that is logically fallacious.  Called the “persuasive definition” or “rhetorical definition,” this occurs when a person uses an established word in a way that is not found in a dictionary or lexicon.  Essentially, a persuasive definition is a false definition.

Often persuasive definitions are used as a short-cut in place of logical reasoning to persuade someone (hence the name).  The idea is to get a person to accept a false definition of a term so that they will also accept a particular idea.  This approach may be effective, but since the definition is false, to use a persuasive definition is dishonest.  Consider the following example:

“Contraception: the deliberate prevention of unwanted pregnancy so that families may be able to give more time, care, and money to their extant children, their community, and to God.”
Of course, this supposed definition of ‘contraception’ will not be found in any dictionary.  The first part of it might be, but the second part has been smuggled into the “definition” in order to influence the reader to think in a positive way about contraception.  There would be nothing wrong with someone making a legitimate argument for the benefits of contraception, but it is dishonest to state the above as the definition of the term because it is not the definition.  Conversely, someone who is against contraception might try the following persuasive definition:

“Contraception: the willful interference of God’s plan for humankind to go and multiply.”

Clearly, the person arguing this way wants to persuade others that contraception is contrary to God’s plan.  Again, someone might make a legitimate argument for this position.  But it would be dishonest to claim that the above is the definition of contraception, because it is not.

A persuasive definition might be a true statement if it were not stated as a definition.  For example, “An atheist is someone who knows that God exists, but verbally denies it.”  That is actually a true statement in light of Romans 1:18-20.  But it is not the definition of ‘atheist’, and it would therefore be dishonest to present it as the definition of the term.  The definition of ‘atheist’ is “a person who believes there is no God.”  We may want to persuade someone of the (correct) position that in fact everyone knows God but some people suppress that truth in unrighteousness.  And there are legitimate, logical arguments we could use.  But stating an incorrect definition is not one of them.

Persuasive definitions are often, though not always, used to defend a position that is false.  Since a false position cannot be defended rationally, the advocate is forced to use irrational or dishonest means to persuade others.  Redefining terms in a way not found in the dictionary is a common approach because (unfortunately) it often works.  Beware of such irrational rhetoric, and always consult a dictionary to be sure.

As a last resort, a buffoon might try to defend his use of a persuasive definition by declaring, “the dictionaries are wrong!  The word actually means what I said it means!”  The silliness of this position is quickly revealed when we consider that it could be used to “prove” things that are false!  Suppose I held a piece of chalk in my hand and declared “This is a dinosaur.  See, it is white, flaky, and can be used to draw on a chalkboard.  Clearly, it is a dinosaur.”  Someone might respond, “No, it’s a piece of chalk.  The dictionary defines ‘dinosaur’ as a group of extinct reptiles.”  “Ah,” responds the buffoon, “but the dictionary is wrong.  It has the incorrect definition of both ‘chalk’ and ‘dinosaur.’”

Similarly, if we are allowed to deviate from the dictionary, then we can prove absolutely anything no matter how absurd, by simply defining it as such.  Do you want to prove that the moon is made of green cheese?  No problem.  Simply define “green cheese” as “the substance that comprises the moon” and say that the dictionaries are wrong.  Do you want to prove that the earth is a flat square resting on a giant turtle?  Simply define the earth to be “a flat square resting on a giant turtle.”  Then your statement will be true by definition!  But, of course, it is a false definition.

The dictionary records the way people use words.  When a person says, “The dictionary is wrong” he really means “I refuse to use words in the same way other people do.”  If followed consistently, this would make it impossible for the person to communicate with others, because successful communication requires both the sender and recipient to use words in the same way.

The Ends Do Not Justify the Means

Some people love to use persuasive definitions because they are effective.  You might genuinely succeed in persuading someone of your position by redefining terms in a biased way.  But it would be dishonest.  An evolutionist might succeed in persuading someone to believe in Darwinian evolution by referring to bacteria that have become resistant to antibiotics as an example of “evolution.”  But this is a bait-and-switch fallacy.  Sadly, some creationists also prefer to simply redefine terms in order to persuade people of biblical creation.  Using a false definition may indeed persuade many.  But is the Lord pleased when His children are dishonest in order to achieve a commendable goal?  Does the Bible encourage us to lie in order to persuade people to believe the truth?

A more ethical approach is to use words as they are commonly used by people so that the meaning is clear.  Persuasive definitions cloud clear communication and inhibit logical reasoning.  They are dishonest, but God is a God of truth.  We have a moral obligation to communicate only truth and to do so with clarity.  It is therefore essential to define any ambiguous terms at the outset of our conversation, to define them correctly, to clarify with a precising definition if needed, and to use those words consistently throughout.

The famous Hymn writer Isaac Watts was not only a gifted theologian, but also an expert on logic.  He wrote a textbook on the topic entitled “Logic: The Right Use of Reason in the Inquiry After Truth.”  The book was used as a standard textbook in schools for nearly two centuries.  In chapter 6 Watts gives wise advice on this topic.  He states, “When we communicate our notions to others… let us, in the beginning of our discourse, take care to adjust the definitions of names wheresoever there is need of it; that is, to determine plainly what we mean by the chief words which are the subject of our discourse; and be sure always to keep the same ideas, whensoever we use the same words, unless we give due notice of the change.”  Clearly, it is crucial to define important terms and use them consistently.  And we should avoid ambiguous words when possible.

Watts goes on to state, “But where there is a necessity of using an ambiguous word, there let double care be used in defining that word, and declaring in what sense you take it.”  This is why I often refer to evolution as “Darwinian evolution” or “particles-to-people evolution” so that the reader may understand exactly what I mean.  But evolutionists violate this principle of logic when they conflate “evolution” in the sense of any generic chance with “evolution” in the sense of common descent.  It may be persuasive.  But it is both illogical and immoral.

Correct usage of words not only helps us to communicate successfully with others, but it also helps us to avoid errors in our own reasoning.  We generally use language in the process of thinking.  So, incorrect use of language can lead to incorrect thinking.  To be logical, we need to use the correct definitions of words, and to use those words in a consistent fashion.