Linguists refer “duality” (of structure) to the fact that in all languages so far investigated, one finds two levels of structure or patterning. At the first, higher level, language is analyzed in terms of combinations of meaningful units (such as morphemes, words etc.) ; at the second, lower level, it is seen as a sequence of segments which lack any meaning in themselves, but which combine to form units of meaning. According to Hu Zhanglin et al. (p.6) , language is a system of two sets of structures, one of sounds and the other of meaning. This is important for the workings of language. A small number of semantic units (words), and these units of meaning can be arranged and rearranged into an infinite number of sentences (note that we have dictionaries of words, but no dictionary of sentences!). Duality makes it possible for a person to talk about anything within his knowledge. No animal communication system enjoys this duality, or even approaches this honour.
1.5.What is productivity?
Productivity refers to the ability to the ability to construct and understand an indefinitely large number of sentences in one’s native language, including those that has never heard before, but that are appropriate to the speaking situation. No one has ever said or heard “A red-eyed elephant is dancing on the small hotel bed with an African gibbon”, but he can say it when necessary, and he can understand it in right register. Different from artistic creativity, though, productivity never goes outside the language, thus also called “rule-bound creativity” (by N.Chomsky).
1.6.What is displacement?
“Displacement”, as one of the design features of the human language, refers to the fact that one can talk about things that are not present, as easily as he does things present. In other words, one can refer to real and unreal things, things of the past, of the present, of the future. Language itself can be talked about too. When a man, for example, is crying to a woman, about something, it might be something that had occurred, or something that is occurring, or something that is to occur. When a dog is barking, however, you can decide it is barking for something or at someone that exists now and there. It couldn’t be bow-wowing sorrowfully for dome lost love or a bone to be lost. The bee’s system, nonetheless, has a small share of “displacement”, but it is an unspeakable tiny share.
1.7.What is cultural transmission?
This means that language is not biologically transmitted from generation to generation, but that the details of the linguistic system must be learned anew by each speaker. It is true that the capacity for language in human beings(N. Chomsky called it “language acquisition device”, or LAD) has a genetic basis, but the particular language a person learns to speak is a cultural one other than a genetic one like the dog’s barking system. If a human being is brought up in isolation he cannot acquire language. The Wolf Child reared by the pack of wolves turned out to speak the wolf’s roaring “tongue” when he was saved. He learned thereafter, with no small difficulty, the ABC of a certain human language.