Sentence:  And although these insights into the nature of art may be 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 <WSD>valid</WSD> chapters in the philosophy of art may be written . 
Meaning of the word marked with <WSD> tags:  well grounded in logic or truth or having legal force