Rules of Word Formation (Morphology)
All human languages, including signed languages, exhibit rules of word formation (morphology). A morpheme is an irreducible unit of meaning in a given language. It can be either a word itself (mean) or a meaningful part of a word (-ing, -ful, the vowel in the past tense of read, the alternating stress pattern in the noun and verb forms of record, etc.). Morphemes that have syntactic consequences are referred to as “inflectional”; these include morphemes of tense (past tense –ed), aspect (continuous –ing), person (3rd singular –s), number (plural –s), gender (lion + ess), case (he vs. him vs. his), etc. Morphemes are called “derivational” if they change the grammatical category (part of speech) of a word – e.g. derive (v.) + ation (n.) + al (adj.) – or alter the basic meaning of a word – e.g. un + do, re + do. Signed languages exhibit both inflectional and derivational morphemes. There is no evidence for any such system in animal communication. The closest documented behavior in naturally occurring animal communication is the use by male Campbell’s monkeys of a low-pitched “boom” preceding a predator alarm call to indicate that danger is not imminent. In trained animal communication, there is no evidence of any primate or non-primate ever having mastered any aspect of linguistic morphology. In particular, so-called “signing” apes have never acquired either the comprehension or the production of any aspect of sign language morphology.