Sentence:  Whitehead is here questioning David Hume 's understanding of the nature of experience ; he is questioning , also , <WSD>every</WSD> epistemology which stems from Hume 's presupposition that experience is merely sense data in abstraction from causal efficacy , and that causal efficacy is something intellectually imputed to the world , not directly perceived . 
Meaning of the word marked with <WSD> tags:  (used of count nouns) each and all of the members of a group considered singly and without exception