The concept that the simplest explanation for a phenomenon is the best one, that is, “what can be done with fewer (assumptions) is done in vain with more.”
Philosophical rule first put forth by the medieval English scholar William of Occam or Ockham (c. 1285-1349). “Occam’s Razor,” sometimes called the “law of parsimony,” states that explanations for a phenomenon should be simple and should not be multiplied without a very good reason: “Entities must not needlessly be multiplied.” In other words, the simplest explanation is to be preferred over more complex explanations. When faced with two hypotheses that explain the observations equally well, choose the simpler. Observers should try to explain unusual happenings as the result of known phenomena, rather than assuming that they occur from new or exotic causes.
Occam’s Razor is a useful tool for philosophical thinking because it places logical limits on the possible number of explanations for any given happening. One example might be the space theories of Immanuel velikovsky: they offer complex ideas that might be true, but only if a very complex chain of events had taken place. Occam’s Razor suggests that a simpler explanation would be more likely.