“With all things being equal, the simplest explanation tends to be the right one.”
“All things being equal, the simplest solution tends to be the best one.”
“Keep things simple.”
“Entities should not be multiplied beyond necessity.”
“Entia non sunt multiplicanda praeter necessitatem.”
“Pluralitas non est ponenda sine neccesitate. (Entities should not be multiplied unnecessarily.)”
“The explanation requiring the fewest assumptions is most likely to be correct.”