Ockam’s Razor is normally stated:
“Among competing hypotheses, the hypothesis with the fewest assumptions should be preferred.”
Also known by the Latin “lex parsimoniae” the heuristic is attributed to William of Ockham (also Occam) who was a Franciscan friar (1287–1347) and an influential medieval philosopher (see first link below). However, the form of words attributed to him:
“entities must not be multiplied beyond necessity”
do not appear in his writings!
Thomas Aquinas (1225–1274) wrote:
“it is superfluous to suppose that what can be accounted for by a few principles has been produced by many”.
Much earlier Claudius Ptolemy (circa 90–68) wrote
“we consider it a good principle to explain the phenomena by the simplest hypothesis possible”.
All these formulations converge on the same idea:
Simpler explanations are, all other things being equal better than more complex ones.
The idea is intuitively sound. Why add unneeded complications? However, this does not mean the simpler explanation will always be better. The heuristic has been extensively investigated (see second link below) and has proved very useful as a guide to more likely explanations that in turn need to be validated by other methods. Its general usefulness in many fields of endeavour is more than enough justification to adopt it as a guide to understanding.
Ockham’s razor, also known as the Principle of Parsimony, is in practice applied in science as the and is widely used to guide research. In day-to-day life the heuristic can be used to evaluate other people’s explanations of events but whilst it should not be viewed as a physical law, it is however a very useful rule-of-thumb.
One example of the benefits of applying Ockham’s razor is that it tends to eliminate most conspiracy theories as too complicated, which again would suggest the heuristic has value.
When presented with several competing explanations with little otherwise to differentiate them, it would seem wise to investigate the simplest first and only discard that explanation if other factors invalidate it. Also, where there is a single explanation that is complex and/or relies on too many other assumptions, then it would be wise to treat it with a certain amount of scepticism.