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.

Plurality should not be assumed 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.

The explanation requiring the fewest assumptions is most likely to be correct.

No more things should be presumed to exist than are absolutely necessary.

With all things being equal, the simplest explanation tends to be the right one.

3 is a prime, 5 is a prime, and 7 is a prime. Why bother with non-prime numbers when the primes can do everything?