Sentence:  The joint investigations of linguistics and psychiatry have established , in point of fact , that no matter what the subject of conversation is or what words are involved , it <WSD>is</WSD> impossible for people to talk at all without telling over and over again what sort of people they are and how they relate to the rest of the world . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)