How to define a term

Dr Ben Holloway, Professor of Philosophy and History of Ideas, Southeastern Baptist Theological Seminary

In the following series of posts, I am going to focus on various skills one needs to do philosophy. Most of what I’ll say will be about arguments, what kinds there are and what makes any of them good. Before turning to arguments, we need to spend some time considering the language we use to make them (and understand them). We will begin with definitions.

Why We Need Definitions

When I was about ten, I was staring out the window and paying no attention to my teacher who was talking about a recent accident at sea. “Holloway!” my teacher barked. “Where did the ship sink?” My teacher was fully aware of my inattention and was going to show me up. I had no idea where the ship had sunk. So, I answered a different question. I told him where the ship had sprung a leak. “In the hull, sir,” I replied. My teacher was taken aback and turned to the class. “Holloway is correct, the ship sunk in Hull.” (1)

On that occasion, the messiness of natural language worked in my favour, but it often doesn’t. Natural languages can be difficult to use. We can’t always say what we mean, and we don’t always understand each other. Precision and clarity in language is vital for correct thought. And if correct thought is what we are after, we’d better do some work on language. We’ll begin with terms, words or phrases that can serve as the subject of a sentence.

What Definitions are For

As my example shows, terms can be ambiguous. They can have multiple meanings. Hull either means a port city in Humberside, or it is the body of a ship or boat. (2) Theological discourse is filled with ambiguous terms. Grace can mean undeserved favour or a beautiful movement. Faith can mean the mental state of belief, trust in a person, or the contents of what we believe. James uses the first meaning, Jude, the last. To disambiguate a term, one usually requires knowledge of how it is used by a community of language users. Lexicons list the various uses and, by considering which use makes best sense in its context, we can usually favour one interpretation over another. Occasionally, the evidence is not conclusive. Disagreement over interpretations have far-reaching consequences for theology. For example, a debate over the meaning of Paul’s use of the term, justification, can have enormous effects on the doctrine of salvation.

Language can also be vague. Goliath is supposed to be a ‘giant.’ But how tall does one have to be to count as a giant? Without further information, we can’t be certain. It often depends on the context. I am six foot one. I am tall in London, but short in Minnesota. I am thoroughly persuaded by J. Daniel Hays who argues that Goliath was 6’9″ based on the LXX version of the text. (3) When one discovers that the height of the Israelite averages just over 5′, it is easy to see why he might have been considered a giant. Terms that are vague require sharpening. Precise definitions would tell us what counts as soon, tall, poor, heavy, or expensive.

Sometimes we want to talk about something that hasn’t been talked about before. Consequently, we need a new word or phrase with a new definition. A stipulative definition is a definition supplied for the first time. New terms are ‘coined’ all the time, especially during the production of new technology. They are also produced by legal judgments. A court may stipulate a definition for a term for legal reasons. Often stipulated legal definitions are at odds with moral judgments leading to difficult interviews in which a political candidate is prepared to defend a law even when it is at odds with her moral views. (4)

In our era of fraught political debate, we are used to hearing persuasive definitions. This kind of definition is given to influence a person’s attitude toward a term. Suppose I ask you to define ‘social media’ in a way that might put someone off using it. You might say, social media is a mind-sucking, divisive medium intended to control the thoughts of the population. We often define ‘abortion’ as slaughter of children in the womb. It is a persuasive definition because it attempts to bring out the grim reality of the action.

Sometimes, persuasive definitions have the opposite effect. They serve to shut down debate before it can begin. They should be used carefully. Words can be clear means of communicating, but they can also be hammers with which to bash an opponent. Quite a few of the terms we use have no clear meaning, but instead serve to express one’s feelings on a matter. Political discourse is often more expressive than cognitive. We use terms such as ‘woke,’ ‘nationalist,’ ‘lib,’ ‘lefty,’ ‘tory,’ and alike without clear ideas of what we mean. They are used, instead, to express distaste. It is not that they can’t have clear meanings. Rather, language admits uses of terms for expression rather than communicating cognitive content.

How to Make a Definition

Although expression of feelings has its place, the better we use language to communicate cognitive content, the better we serve our cause. One virtue we should seek is clarity. And to be clear in what we say, we need to provide definitions for the terms we use in expressing what we think. Loosely speaking, a definition gives the meaning (or sense) of a word or phrase. The definition of a term usually has intension and extension. The intension of a term is the sum of the properties common to the entities to which the term applies. The extension of a term is the list of entities to which it applies. For example, the intension of ‘a book’ will include ‘has pages with words on them that are bound together.’ The extension will include all things which satisfy the intension such as ‘textbooks, my book, novels, manuals, etc.’ When offering a definition, clarity is often achieved by clearly stating the intension followed by providing examples from its extension. We don’t always start with a term’s intension. For example, children learn their first words by hearing them accompanied by a parent pointing at something. “Mummy,” mum says while pointing at herself. On other occasions we might list the extension of a term. For example, we might say that the Bible means Genesis, Exodus, Leviticus and so on. Alternatively, we might list an extension of a term by its kinds. For example, we might say that theology means biblical, historical, exegetical, and systematic studies.

There are a variety of ways to get at the intension of a term. Etymological definitions give the origin and historical use of a term in both its own language and other languages. Occasionally, etymological definitions are helpful. An example is the English word ‘captain,’ which derives from the Latin noun caput, meaning head. Other etymologies are less useful. ‘Atonement’ is derived from an older form of English and meant being in a state of harmony. But the term’s etymology fails to capture what we mean when it is used in theological discourse.

One might want to offer a theoretical definition according to which one states which theory of the atonement one supports. For example, one might define the atonement as the penalty paid by Christ on our behalf. Theoretical definitions are common in science. For example, H2O is a theoretical definition used for water to give a theory of the elements of which it is composed. There are two common strategies for making definitions that are especially useful. In my experience, it is best to start with one and, if it fails, to turn to the next. By far the simplest and most effective technique for defining a term is to supply a definition of a term’s genus and difference. The genus of a term tells us what category the concept falls under, and the difference of a term tells us what differentiates it from all the other concepts in that category. Take the word, ice. Ice falls under the genus of water. Water can be liquid, gas, or solid. What makes the solid kind of water different to the others is that it is frozen. Hence the definition of ice is frozen [difference] water [genus].

Let’s try a couple of other examples. I live in a state (North Carolina) whose inhabitants are fond of pick-up trucks. Suppose we want to offer a definition of pick-up truck using its genus and difference. First, ask yourself what kind of thing a pick-up truck is. You might come up with motor vehicle. Then, list all the other things in that category. You might list cars, motorcycles, and SUVs. Now ask yourself what makes the pick-up truck different to all the other things on that list. My students in the US instantly tell me that pick-up trucks have ‘beds.’ So, you could define a pick-up truck as a motor-vehicle with a bed. Of course, ‘bed’ is ambiguous, so you might like to provide a definition of that too!

How about a more theological term? For example, how should we define salvation? What is a good definition by genus and difference? Here is one way to define it. Salvation is a kind of deliverance from something. We can be delivered from the threat of an opposing army or from prison or from sickness. In a theological context, what we mean by salvation is a deliverance from the wrath of God.

Some terms are very difficult to define by genus and difference. If you cannot think of a way to do it, such terms may be handled by supplying an operational definition. An operational definition assigns meanings to words by specifying certain experimental procedures that determine whether the word applies to a certain thing. Making use of an operational definition for theology is helpful especially when talking about processes and events which take place in the lives of believers. For example, consider the term, ‘conversion.’ If you play rugby, you will notice that the term is ambiguous. In rugby, conversion is the act of scoring extra points after scoring a try. In theological contexts, we mean something different. One could provide a definition by genus and difference. Perhaps we might describe conversion as a kind of process in which a person adopts a religion. But we probably need something more precise. We want to know what happens when someone converts to Christianity. We may want a definition that makes explicit the conditions under which conversion has occurred. In his book, Conversion in the New Testament, Richard Peace provides an operational definition for conversion. (5) According to Peace, a person has experienced a conversion when that person has received insight, turned from his old life to Jesus, and has a transformed life.

Another term which is difficult to define by genus and difference is culture. Just what kind of thing is culture? Is it a kind of set of beliefs? And if one can get this far, it is difficult to find a good set of differences to distinguish it from others of its kind. Consequently, we may be better off with an operational definition. After all, culture is something that occurs when we are doing something. If we ceased to make art, educate our children, establish political and cultural institutions, culture would cease. So, for what purpose do we do all these activities that would make them cultural activities? Most plausibly, we do them to pass on beliefs, norms, and practices from one generation to the next.

How does this help provide a definition for culture? If we employ an operational definition, we can say that culture occurs when people pass on their beliefs, norms, and practices from one generation to the next. (6) Occasionally, things work in the other direction. A notoriously difficult term to define is ‘person.’ But having a good grasp of what we mean by person is vital for our ethical positions on issues such as abortion. Notice what happens if we try to use an operational definition. We might say that a human is a person when it is self-aware, conscious, capable of sustaining its life on its own. In fact, proponents of abortion will almost always use an operational definition. They will suggest that unless the conditions of their definition are met, the human life in the womb is not a person, in which case it does not possess a right to life. Consequently, it is crucial to try to provide a definition either that is not operational or that includes a newly conceived egg.

Here is one way to provide such a definition suggested by John Feinberg and his brother, Paul. The Feinbergs suggest that we define a human person as a living being made in the likeness of God. (7) No other organism made by God is said to be made in His image. This is what differentiates humans from all other animals. God qualifies as the paradigm of person and possesses all the characteristics of self-awareness and self-determination we’d expect in a person. In virtue of being made in his image, human beings also count as persons. Notably, image-bearing, and consequently, personhood comes with existence. We don’t acquire it after our conception. And it doesn’t require any proof of possession. If an image bearer exists (i.e., a human being), it is a person. Since a human being exists at the point of conception, it is a person at that point too. Involving one’s theology in a definition may sound suspect to a nonbeliever, but it is not an illegitimate thing to do when supplying a definition. (8)

Some terms are so difficult to define, we consider their concepts to be ‘open.’ In other words, we don’t have a clear intension for the term, so we can allow for our concepts to admit variance over time. We might include things in the extension because they resemble other things already admitted without having to provide a precise intensional sense for a word. A famous example provided by Ludwig Wittgenstein is ‘game.’ (9) Just try to define it so precisely that you include all the things we think are games and exclude the things we think aren’t. Other terms which defy precise definitions and may be open concepts are ‘art’ and ‘science.’

The words we use are important, but they can’t assert anything about the world. Hence, words aren’t the only thing we must master if we are to gain any skill with arguments. Only certain kinds of sentences can do the work of expressing truths about the world. It is to those we turn next.


  1. For my international readers, Hull (an abbreviation of Kingston on Hull) is a port in the North of England.
  2. I am aware that Humberside is no longer a thing, but it was when I made my lucky escape from my teacher’s wrath.
  3. J. Daniel Hays, “Reconsidering the Height of Goliath” Journal of the Evangelical Theological Society 48 (2005): 701–714.
  4. The term ‘marriage’ has both a legal and a moral or religious sense.
  5. Richard Peace, Conversion in the New Testament (Grand Rapids: Eerdmans, 1999).
  6. This definition is used by Theodore Gracyk, The Philosophy of Art: An Introduction (Malden, MA: Politity Press, 2012), 94.
  7. John Feinberg and Paul Feinberg, Ethics for a Brave New World (Wheaton: Crossway, 2010), 88.
  8. The Feinbergs’ definition is notably different to the other examples. It is a recursive definition, according to which there is a ‘base case’ for a concept and then a relation to the base case which bestows membership to others. For example, a definition for citizen might be “S is a citizen iff (1) S has passed the citizenship test, or (2) S is the child of a citizen.” The base case is found in (1), but a member of the category described in (2) is granted membership to citizenship through a relation to the base case. Analogously, God serves as the ‘base case’ in the Feinbergs’ definition and human beings are granted membership by being image bearers. The citizen example is given by Richard Feldman, Epistemology (Upper Saddle River, NJ: Prentice Hall, 2003), 91–92.
  9. Ludwig Wittgenstein, Philosophical Investigations (Upper Saddle River, NJ: Prentice Hall, 1958), 32, §67.