In metaphysics
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

, impenetrability is the name given to that quality of matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

 whereby two bodies cannot occupy the same space at the same time
Pauli exclusion principle
The Pauli exclusion principle is the quantum mechanical principle that no two identical fermions may occupy the same quantum state simultaneously. A more rigorous statement is that the total wave function for two identical fermions is anti-symmetric with respect to exchange of the particles...

. The philosopher John Toland
John Toland
John Toland was a rationalist philosopher and freethinker, and occasional satirist, who wrote numerous books and pamphlets on political philosophy and philosophy of religion, which are early expressions of the philosophy of the Age of Enlightenment...

 argued that impenetrability and extension
Extension (metaphysics)
In metaphysics, extension is, roughly speaking, the property of "taking up space". René Descartes defines extension as the property of existing in more than one dimension. For Descartes, the primary characteristic of matter is extension, just as the primary characteristic of mind is consciousness...

 were sufficient to define matter, a contention strongly disputed by Gottfried Wilhelm Von Leibnez
Gottfried Leibniz
Gottfried Wilhelm Leibniz was a German philosopher and mathematician. He wrote in different languages, primarily in Latin , French and German ....


John Locke
John Locke FRS , widely known as the Father of Liberalism, was an English philosopher and physician regarded as one of the most influential of Enlightenment thinkers. Considered one of the first of the British empiricists, following the tradition of Francis Bacon, he is equally important to social...

 considered impenetrability to be "more a consequence of solidity
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...

, than solidity itself."[2]
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.