Mental substance is the idea held by dualists and idealists, that minds are made-up of non-physical substance. This substance is often referred to as consciousness.
This is opposed to the materialists, who hold that what we normally think of as mental substance is ultimately physical matter (i.e., brains).
Descartes, who was most famous for the assertion "I think therefore I am," has had a lot of influence on the mind-body problem.
He used a more precise definition of the word "substance" than is currently popular: that a substance is something which can exist without the existence of any other substance. For many philosophers, this word or the phrase "mental substance" has a special meaning.
Gottfried Leibniz, belonging to the generation immediately after Descartes, held the position that the mental world was built up by monads, mental objects that are not part of the physical world.
Famous quotes containing the words mental and/or substance:
“... work is only part of a man’s life; play, family, church, individual and group contacts, educational opportunities, the intelligent exercise of citizenship, all play a part in a well-rounded life. Workers are men and women with potentialities for mental and spiritual development as well as for physical health. We are paying the price today of having too long sidestepped all that this means to the mental, moral, and spiritual health of our nation.”
—Mary Barnett Gilson (1877–?)
“Ah, to build, to build!
That is the noblest art of all the arts.
Painting and sculpture are but images,
Are merely shadows cast by outward things
On stone or canvas, having in themselves
No separate existence. Architecture,
Existing in itself, and not in seeming
A something it is not, surpasses them
As substance shadow.”
—Henry Wadsworth Longfellow (1807–1882)