In this section we shall give some account of Whitehead's notion of a prehension,¹ which is a key concept in his later philosophy. He sometimes uses the term feeling as a synonym, which as thus used has a more general sense than it has in our ordinary use, where it specifically refers to our subjective affective states. Whitehead extends its meaning so as to describe both physical and psychological processes: simple physical feelings are also regarded by him as descriptive of energy changes in the physical world.