Sentence:  And although these insights into the nature of art may <WSD>be</WSD> in themselves insufficient for a thoroughgoing philosophy of art , their peculiar authenticity in this day and age requires that they be taken seriously and gives promise that from their very substance , new and valid chapters in the philosophy of art may be written . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)