Sentence:  And although these insights into the nature of art may be in themselves <WSD>insufficient</WSD> 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:  of a quantity not able to fulfill a need or requirement