The definist fallacy (sometimes called the Socratic fallacy, after Socrates)[1] is a logical fallacy, identified by William Frankena in 1939, that involves the definition of one property in terms of another.[2]
The philosopher William Frankena first used the term definist fallacy in a paper published in the British analytic philosophy journal Mind in 1939.[3] In this article he generalized and critiqued G. E. Moore's naturalistic fallacy, which argued that good cannot be defined by natural properties, as a broader confusion caused by attempting to define a term using non-synonymous properties.[4] Frankena argued that naturalistic fallacy is a complete misnomer because it is neither limited to naturalistic properties nor necessarily a fallacy. On the first word (naturalistic), he noted that Moore rejected defining good in non-natural as well as natural terms.[5]
Frankena rejected the idea that the second word (fallacy) represented an error in reasoning – a fallacy as it is usually recognized – rather than an error in semantics.[6] In Moore's open-question argument, because questions such as "Is that which is pleasurable good?" have no definitive answer, then pleasurable is not synonymous with good. Frankena rejected this argument as: the fact that there is always an open question merely reflects the fact that it makes sense to ask whether two things that may be identical in fact are.[7] Thus, even if good were identical to pleasurable, it makes sense to ask whether it is; the answer may be "yes", but the question was legitimate. This seems to contradict Moore's view which accepts that sometimes alternative answers could be dismissed without argument; however, Frankena objects that this would be committing the fallacy of begging the question.[6]
