Rules of Phrase/Sentence Formation (Syntax)
All human languages have rules for combining words into phrases and sentences. These are crucial for encoding and deciphering the composite meaning of an utterance. Particular rules vary across populations both within and across languages, but are also recognized as displaying certain universal tendencies that fall within a limited range of possibilities. There is limited evidence for constraints governing the combination of individual acoustic elements in primate systems of vocalization – based primarily on transitional probabilities within long call systems and playback experiments that exploit them – in that the resulting behavior of primates will differ from the norm in a particular context when normal transitional probabilities are altered. There is for the most part no evidence of language-trained apes ever acquiring or generating rule-governed behavior for combining lexical elements of the system in which they were trained. The one possible exception is the case of a language-trained bonobo who statistically preferred using symbols from an artificial language before using indexical pointing gestures in utterances that combined artificial symbols and indexical points; this sequencing was not present in the communications of his trainers. There are several reports of meaningful two-sign combinations in language-trained apes, but these are disputed. Larger combinations in language-trained ape output consist of either repetitive chaining/cycling of the same elements or apparently random and therefore nearly impossible-to-decipher juxtapositions.