Full Idea
A plurality is a denumerable quantity, and a magnitude is a measurable quantity. A plurality is what is potentially divisible into things that are not continuous, whereas what is said to be a magnitude is divisible into continuous things.
Gist of Idea
Pluralities divide into discontinous countables; magnitudes divide into continuous things
Source
Aristotle (Metaphysics [c.324 BCE], 1020a09)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.134
A Reaction
This illuminating distinction is basic to the Greek attitude to number, and echoes the distinction between natural and real numbers.