The paper tries to separate two opposite features of natural languages. Plato was the first who had noticed both of them. The one characteristic of languages, well known to the logicians and all scientists consists in the capability of languages to name things and to define meanings and accordingly to communicate positive ideas and unambiguous concepts. The second one is connected with the evolutionary features. It is relatively hidden and for us it is not easy to see its nature. It rests upon the operation of the delimitation of ideas during the process of understanding.