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:
“A major misunderstanding of child rearing has been the idea that meeting a child’s needs is an end in itself, for the purpose of the child’s mental health. Mothers have not understood that this is but one step in social development, the goal of which is to help a child begin to consider others. As a result, they often have not considered their children but have instead allowed their children’s reality to take precedence, out of a fear of damaging them emotionally.”
—Elaine Heffner (20th century)
“All the old supports going, gone, this man reaches out a hand to steady himself on a ledge of rough brick that is warm in the sun: his hand feeds him messages of solidity, but his mind messages of destruction, for this breathing substance, made of earth, will be a dance of atoms, he knows it, his intelligence tells him so: there will soon be war, he is in the middle of war, where he stands will be a waste, mounds of rubble, and this solid earthy substance will be a film of dust on ruins.”
—Doris Lessing (b. 1919)