Full Idea
There are two ways that entities can be multiplied unnecessarily: by multiplying the number of explanatory categories, and by multiplying the number of entities within a category.
Gist of Idea
Entities can be multiplied either by excessive categories, or excessive entities within a category
Source
J Hoffman/G Rosenkrantz (Platonistic Theories of Universals [2003], 4)
Book Reference
'The Oxford Handbook of Metaphysics', ed/tr. Loux,M /Zimmerman,D [OUP 2005], p.69
A Reaction
An important distinction. The orthodox view is that it is the excess of categories that is to be avoided (e.g. by nominalists). Possible worlds in metaphysics, and multiple worlds in physics, claim not to violate the first case.