Definition of Occam's razor

Occam's razor: The principle of scientific or, in medicine, diagnostic parsimony or "unitarianism." In medicine, a clinician would like to be able to use Occam's razor and come up with a unifying diagnosis that will explain all of the patient's problems. "Although we generally like to invoke Occam's razor, for some patients we cannot follow the rule of diagnostic parsimony." (New Engl J Med 350: 600, 2004). William of Occam in the 14th century stated this principle: "The assumptions introduced to explain a thing must not be multiplied beyond necessity."