The standard textbook accounts of language say that specific languages such as French or German consist of three components: a phonological component that determines how words and sentences are pronounced, a syntactical component that determines the arrangement of words and morphemes in sentences, and a semantic component that assigns a meaning or interpretation to words and sentences.
So, for example, when you change a sentence around, the words (and morphemes) do not lose their identity.
Unlike baking a cake where the ingredients are changed by being mixed together, forming a sentence does not change the words and morphemes that are being mixed together; and you can have a sentence containing eight words or twelve words, but you cannot have a sentence containing nine and a half words.
Syntactically, a complex element such as a sentence is built up out of simple elements, words and morphemes, according to the formation rules of the language.
That is another way of saying that the hominids need to evolve elements that correspond to our words and morphemes and to ways of combining these into sentences in a compositional manner, in a way that enables the participants to figure out the meaning of the sentences from the meanings of the elements and their arrangement in the sentence.
The paradox is: how do we achieve the unity of the sentence (and hence the unity of the expressed proposition) when the sentence is entirely composed of discrete entities, the string of words and morphemes that constitute it?
Just as every language has an unlimited number of syntactic structures built from a finite collection of morphemes, every language has an unlimited number of phonological structures, built from a finite repertoire of phonetic segments.
As noted as early as Hockett (1960), “duality of patterning”—the existence of two levels of rule-governed combinatorial structure, one combining meaningless sounds into morphemes, the other combining meaningful morphemes into words and phrases—is a universal design feature of human language.
But most words (as well as smaller morphemes such as affixes) can combine into complex words such as compounds (e.g. armchair) and other derived forms (e.g. squeezability) according to principles of the component of language called morphology.
Moreover, functional morphemes such as articles, auxiliaries, and af?xes are also part of the lexicon (since each involves a pairing between a sound and some other information, both of which are speci?c to the particular language), yet the information they encode (case, agreement, ?niteness, voice, and so on) is continuous with the information encoded by syntax.