Plurality is not to be posited without necessity.
When you have two competing theories that make exactly the same predictions, the simpler one is the better.
Entities must not be multiplied beyond necessity.
No more things should be presumed to exist than are absolutely necessary.
Entia non sunt multiplicanda praeter necessitatem
Pluralitas non est ponenda sine necessitate. A plurality (of reasons) should not be posited without necessity.