Language is a highly elaborated signaling system. We call the aspects that are peculiar to it the design features of language. Some of these we find only with the language of human beings, others we have in common with animals. Another aspect of human language is that we express thoughts with words.
A principle feature of human language is the duality of patterning. It enables us to use our language in a very economic way for a virtually infinite production of linguistic units. How does this principle work?
All human languages have a small, limited set of speech sounds. The limitation derives from the restricted capacity of our vocal apparatus.