What linguists call the ‘lexicon’ (from the Greek) is a catalogue of all the words or parts of words or signs or structures consisting of more than one word including metaphors, sayings and idioms, that are known to any given individual and stored in his or her mind. By some usages, when this catalogue is conceived in terms of the number of units listed, it is known as the vocabulary (from the Latin).

It is sometimes believed that a speaker’s capacity for language is defined by the size of his or her vocabulary. But there may be a confusion here. Dictionaries, with the entries in alphabetical order, attempt to reproduce a common lexicon. But a dictionary entry represents only the opinions of the writer or writers and a given theory of the lexicon. No two individuals are likely to have exactly the same vocabulary.

The human lexicon works about a thousand times better than any non-human version. Humans can learn vast numbers of words and go on doing so throughout life, as they meet new people, take up new interests, and so on. We can standardly and effortlessly access many thousands of words or signs, mostly picked up casually. And new words or signs are constantly being created as new interests, social networks, technologies develop. New entries are constantly being created, as old entries fall out of use, or their meaning or pronunciation changes. For younger speakers, go and say have become synonymous. A human child, by contrast, learns around a word an hour. And the lexicon can be continually added throughout adult life. The difference in size and growth capacity between the human lexicon and the set of meaningful gestures known to chimpanzee suggests that they are different sorts of thing.

By the proposal here, the lexicon originates from the time when human ancestors started to decompose and recompose symbols in such a way that this symbolisation process could be represented both mathematically and biologically and thus entered into the code of life, DNA.

Individual items are categorised by their meaning and form. Expressions like Mummy and Daddy reflect a common role in caretaking or close contact. Childish forms like din din or bow wow reflect an exact or partial repetition of structure. Nothing like these repetitions of structure or conjunctions of related meanings has been reported in the natural communication systems of non-humans. The human lexicon is clearly structured on the basis of this duality of form and meaning. The decomposition by the proposal here works like an index in a computer database. And arguably it is this property of the lexicon which allows it to be freely expanded both by individuals and by society.

The content

What the lexicon contains is a matter of debate. The rather full listing above is a personal opinion. Necessarily, the lexicon contains something of the phonetic form of an item, possibly not the full phonetic form, but enough to allow it to be pronounced. There is debate is about almost all aspects of the lexicon. How much of the detail is stored? Does this include a specification as to the category, as a noun, verb, adjective, some sort of functor? Are expressions and metaphors included? And more.

Many languages have ways of encoding what is known as ‘evidentiality’ or the speaker’s confidence in or certainty about the truth of some proposition. Most European languages have what was once just such a system, known as the ‘subjunctive’, except that it has now become part of the syntax. Old English had just such a system, but it has gradually fallen out of use. Older speakers have a vestige of this in “I demand that he go” with go not goes, and “If I were you….” with go and were as subjunctives. In both of these cases, the subjunctive forms still denote a degree of uncertainty.

Experimentation by children

As part of the learning process, children may ‘experiment’ with forms as they work out which way their target language goes with respect to phenomena such as uncertainty.

How the lexicon and vocabulary are different from language

Whereas the lexicon can be expanded effortlessly, for the overwhelming majority of humans this does not apply to language. The capacity of the grammar is infinite. But from around the age of ten it becomes more and more difficult to learn a new language and sound or look like someone who has used it from birth. This time before the age of ten is often known as the ‘critical period’. There is no critical period for the lexicon. But at any given point, we can only access some finite number of words or signs. The better a form is known the more accessible it is for use in speech, signing or writing. But this does not alter the fact that any given point, for any individual, the lexicon is finite.

Whereas the Faculty of Language is common to all humans who have had a normal life. playing with other children in childhood, going to work in adulthood, etc., irrespective of their privileges, accidents of birth, experiences of education, the individual’s vocabulary varies partly as a function of sociological privilege.