Columbia subject headings:
Metaphysics.
Santayana, George, 1863-1952.
Whitehead, Alfred North, 1861-1947.
Harvard subject headings:
Metaphysics
Santayana, George, 1863-1952.
Whitehead, Alfred North, 1861-1947
Princeton subject headings:
Metaphysics.
Santayana, George, 1863-1952.
Whitehead, Alfred North, 1861-1947.