Claudio Gutierrez 
Translated from Spanish by Inés Gutiérrez
Claudio Gutierrez In previous chapters, while explaining fallacies, we referred to the fact that some language terms are ambiguous, that is, they have at least two meanings. The opposite can also happen, namely, that two different terms have approximately the same meaning. We call such terms synonyms. The pair of terms “jail” and “prison” may serve as a good example. Synonym terms have the same meaning only approximately, since the linguistic history of each of them, the cases where each one is preferentially used, may make their meaning differ somehow either in emotional connotation or in descriptive effect. The term “jail”, for example, seems to refer to a rather small prison. Nevertheless, we can tell someone who does not know the meaning of “jail” that it is a prison, or vice versa, perhaps adding an adjective (e.g. "small" or "large") qualification. We will have given him/her a definition of the specific term.
Definitions are not always given by presenting a synonym of the term. Most of the time we use phrases to explicate the meaning of words. For example, we can say that “single” is an unmarried person. In this case, “single” is the term to be defined (definiendum) and “unmarried person” is the sentence which defines it (definiens). Definiens and definiendum are considered equivalent expressions, in the sense that they have the same meaning. However, this is only approximately true. In common use, “single” and “unmarried man” are not used indistinctly. If I say I am an unmarried man, I am placing emphasis on my sex, which is not present in the word “single”. We already know that emphasis can affect meaning. Nevertheless, a person who is learning a new language will appreciate the giving of (approximate) equivalents between two expressions.
So, we see that definition is a useful utility for the learning and suitable interpretation of language. However it is not –as some people will have it– the very foundation of language. Language is based on our usage of the words; use, not definition, determines meaning. Definitions can undoubtedly show us the way to correct use, but are not sufficient. They are, so to speak, provisional crutches which help a learner of a language to begin deciphering the meaning of the terms. Words only happen in context, as part of propositions, emotional statements, or commands. We only understand a word appropriately if we have become sufficiently familiar with its use in a variety of contexts. The problem is that we only fully understand the context if we understand all the words present in it. We seem to be reasoning in circles! But in fact this is not so, because word context consists of not only other words but of human life in its totality.
The “vicious circle” of the acquisition of meaning is broken by humankind every day: children learn to speak without having any previous knowledge of language. So do in all countries adult immigrants and tourists. In such an undertaking, definitions perform only a small although important function: to give us inkling about words whose meaning we still have to master by experience. The other help that we get is that understanding of new words happens against a shared background, our common human nature. We all have to eat, we all get tired, rejoice, grieve, etc. The characterization supplied by definitions occurs within this grand context of shared biological and social needs and common sense data. It serves us only transitorily, as keys that provide a temporary sense during the acquisition of new terms. Their more permanent sense we will get only gradually, by growing familiar with the practical use of words in many different situations; either experientially or virtually (as by extensive reading).
There are several types of definition. The one which we have been analyzing is called real; it informs us about the concrete qualities of the thing defined by giving us the description of an object in the real world. We may give the following definition for the word “jail”: “A building for confinement of people who have broken the law or are awaiting trial.” This would be a definition of the term “jail”. But we could also say that the thing jail is the building that serves for the confinement etc. Here, although we are indirectly explaining the meaning of a word, we are also directly describing a part of the universe, that is, all the places that the word designates.
Of this kind of definition we can appropriately say that it is true or false; it is an authentic proposition. But it should be noted that a true definition, such as the one for “jail”, cannot be made false through any physical change of the external world, as the proposition “I am writing” would become false the minute I stop writing. The true definition can become false only if the use of the word changes –in this case “jail”–within English speaking people. It could well happen that “jail” will be only used in poetic form (“the jail of your arms”), or referring to moral bindings (“the jail of my sins”). In this event, it would be false to say that “jail” is a place of confinement etc. Properly speaking, then, a definition does not inform us about the physical world –to which it would seem to refer– but about the social world. in one of its perspectives: namely, the linguistic habits of people.
When someone contrives a new term to replace others from ordinary language, defining it with the help of those others, we say that he has given a nominal definition of the new term. This definition is arbitrary, and has nothing to do with established usage. In a certain way, it goes against (current) usage. However, in a rapidly evolving culture, its role becomes more and more important. The advantage of creating new terms is evident in technology, in the most extensive sense of that term: it enhances brevity and precision. Its importance is also invaluable in the exact sciences; using new terms instead of long explanations avoids the ambiguity and emotional connotation of ordinary language, performing an irreplaceable function in teaching and research.
We call this definition nominal, parting slightly from tradition, in order to better emphasize its contrast with real definition. Nominal definition is a definition given by convention, having no direct relation to the real world. It is a term invented to designate something, the expression of which formerly required a long sequence of familiar words, or words inconveniently charged with emotion. As such, this kind of definition can be neither false nor true; it is simply not a proposition. It is rather a command or recommendation, the expression of a resolution to use a symbol in a specific sense. It belongs to directive, not to informative, language. Examples of terms introduced by nominal definition are the names of commercial products or parts of newly invented machinery, codes used within companies to communicate over long distances, mathematical symbols, and many technical terms used in the different sciences and technologies.
Real and nominal definitions are the most distinct, and extreme, types of definition. There are, also, mixed definitions, part real and part nominal. Included among these are explicative definitions. When a term in ordinary language is ambiguous and we need it to be precise, we must provide a definition which exactly determines its field of application. We might be interested in knowing whether a large machine permanently installed at a certain site is, or is not, real property (to decide, for example, whether it is subject to real-estate taxes). This issue can only be solved one way or the other by convention, since the word “property” is sufficiently vague to be used in many different senses. Is “income” the word we must use to designate the profit earned by a land developer when he sells a lot, or rather "equity appreciation"? The I.R.S. and the developer may also have conflicting interests on this issue. Laws and jurisprudence are full of explicative definitions which abide in part in the ordinary usage of words, being real to this degree; and which in part are also arbitrary conventions, to that degree nominal definitions.
We should not confuse definition with another logical figure also possessing an explicative sense, namely, descriptions. Definition explicates the meaning of a collective term, a term applied to many individuals. The term “jail”, for instance, applies to all jails. On defining, we point out the notes or characteristics possessed by every jail object. Descriptions, on the other hand, explain the meaning of a particular name, such as a specific person (“Herod”), place (“Paris”), or certain object (“this particular jail”). If I say that Herod is the villain of the Christmas story, I am not giving a definition but, rather, a concrete description. I am characterizing a certain individual who lived in the first century of our era. The term “Herod” is a proper name, and I can only apply it to a specific person. When in doubt, should many people exist with the same name, e.g. Herod, we resolve the issue by answering the question “Which Herod?” with a description: "The villain of the Christmas story". The same is valid for Paris: "The city of light", or this jail: "Our county's penitentiary". Proper names can only be explicated by means of a description, not by a definition.
Description serves to better locate a unique person or thing; definition, on the other hand, serves to clarify the meaning of general terms, i.e. tokens for many individuals.