Plurality is not to be posited without necessity.

For nothing ought to be posited without a reason given, unless it is self-evident (literally, known through itself) or known by experience or proved by the authority of Sacred Scripture.

What can be explained by the assumption of fewer things is vainly explained by the assumption of more things.

Of two equivalent theories or explanations, all other things being equal, the simpler one is to be preferred.

Entia non sunt multiplicanda praeter necessitatem

Entities must not be multiplied beyond necessity.

Pluralitas non est ponenda sine necessitate. A plurality (of reasons) should not be posited without necessity.