CIRCULUS IN PROBANDO (

Lat. for " circle in proving ")  , in logic, a phrase used to describe a form of argument in which the very fact which one seeks to demonstrate is used as a premise, i.e. as part of the evidence on which the conclusion is based . This argument is one form of the fallacy known as petitio principii, " begging the question." It is most common in lengthy arguments, the complicated character of which enables the speaker to make his hearers forget the data from which he began .