David Kelley on How to Evaluate Definitions

This post relates to trinities podcasts 239 and following. A central theme therein is competing definitions of trinitarian versus unitarian theologies. The ideas in this post are from this textbook, which I used to use in teaching a college course on critical thinking.

A dictionary definition is supposed to be a record of various ways people use certain word. But the sort of definition I’m interested in here is basically classification. It is really concepts that we are trying to define, not words. The point is to sort what those concepts are about into an orderly and sensible scheme, in which there is a place for everything, and everything fits into its own place.

Kelly points out that a good definition should do three things. First it should give us relatively precise boundaries for a concept. Second, it should locate that concept within our classificatory scheme, the structure of genus and species, and it should be found at the correct level of abstractness. Third, a good definition is the first step in summarizing our knowledge of what the concept refers to.

He then suggests six rules for definitions.

1. State the genus and species. For example, a police officer is a government employee (genus) tasked with the general enforcement of laws and with the protection of citizens (species). It would be a mistake, for instance, to define a police officer as a man in New York who carries a stick and a gun. The concept of a man in New York is way too far down our overall classificatory scheme.
2. The definition should be neither too broad nor too narrow. That is to say it should not bring in too many things, nor should it exclude too many things. For example, if I define a religion as a social movement based around worshiping God, that is clearly too narrow, for there are religions which are not based around worshiping God. Or if I define religion as a system of practices which helps to give meaning to people’s lives, that is clearly too broad, as there are such practices which are not religions, such as book clubs or volunteer organizations. Interestingly, a definition can be too broad and too narrow. If I define a domestic dog as a four-legged animal which can be trained to help humans, that excludes naughty or immature dogs (and so is too narrow) on the same time it would include some elephants as dogs (and so is too wide).
3. A definition should state the essential or fundamental or “deep” attributes of what the concept refers to. So if I define a Caucasian person as a typical resident of Vermont, this fails to get at what makes a Caucasian person a Caucasian person.
4. The definition should not be circular. For instance, one cannot define human happiness as the state of a human in which he or she is happy.
5. A definition should avoid negative terms, unless it is a negative concept that we are defining. We can define a Gentile as a human person who is not a Jew, because that is what the term means, but we can’t define a cat as a domestic pet which is not a fish, lizard, a bird, or dog.
6. Finally, the definition should be understandable, intelligible. It should avoid vagueness, obscurity, and metaphor. We should not define a grandma as sort of like a mom but more fun. Nor should we define college as the last hurrah of youth. Of course, some concepts are clearer than others, and many concepts will admit of borderline cases, such as the concept of being mentally handicapped, or the concept of being bald. If a concept is vague, its definition should be about the same, not more vague

Kelly notes that generally if a definition meets the first three criteria, and it will automatically meet the final three criteria.

Now Dr. Branson and I are both trying to sort the unwieldy field of Christian theologies. And both of us would like to use the common and seemingly useful terms “trinitarian” and “unitarian.” Both of us have noticed that these terms were coined in part to express contrary concepts, to reflect mutually exclusive types, so that no theology which is self consistent can go in both categories. Both of us would like our classification to use, as much as is possible, widely understood terms. And both of us are trying to make sense not only of present day theologies, but of the whole history of Christian theologies. Finally, both of us are committed Christians. He is an eastern Orthodox believer, and I am a biblical unitarian Protestant. We have different commitments as to what counts as authoritative sources, and I think this does play a role in this dispute. In any case, the goal of classification is to as it were divide things by their natural joints; one is trying to carve up the reality in question (here, the range of Christian theologies) in a natural, non-arbitrary, and revealing way. Clearly, one can’t say that both of our definitions are correct or even substantially on the right track. Perhaps both of us are badly mistaken, but it is clear that at least one of us is not dividing things up the best way. If you’re following this dispute, then take a look at his definitions using the above criteria. These are perfectly general desiderata for defining, and so are not in any way skewed by theological commitments. If they are good rules, then they should work for definitions in any field, whether geology or biology or linguistics or theology. How do they apply to our definitions?