Its namesake was known as the "venerable inceptor," and wrote such books as the Quodlibeta Septem and the Summa Logicae.  
In psychology, a variant called Lloyd Morgan's Canon exists which explains some animal behavior.  It has been used by 20th century philosophers to attack mind-body dualism, and has been championed by John Smart.  Among its critics are Karl Menger and Walter Chatton, who states that if three pieces of evidence are not enough to justify a proposition, a fourth should be added.   Its namesake was known as the "venerable inceptor," and wrote such books as the Quodlibeta Septem and the Summa Logicae.  FTP, name this statement which is the basis of methodological reductionism, a concept attributed to a 14th century logician which states that entities should not be multiplied without necessity.
In psychology, a variant called Lloyd Morgan's Canon exists which explains some animal behavior.  
Ockham's Razor or principle of parsimony or principle of economy or principle of simplicity (accept equivalents)