Whenever two hypotheses cover the facts, use the simpler of the two.
Of two equivalent theories or explanations, all other things being equal, the simpler one is to be preferred.
No more things should be presumed to exist than are absolutely necessary.
It is vain to do with more what can be done with less.
Entities must not be multiplied beyond necessity.
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?