Sentence:  How literature does this , or for whom , <WSD>is</WSD> certainly not clear , but the content , form , and language of the `` message '' , as well as the source , would all play differentiated parts in giving and molding a sense of purpose . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)