If one concept is defined by another, and the other is defined by the first, this is known as a circular definition, akin to circular reasoning : neither offers enlightenment about what one wanted to know . " It is a fallacy because by using a synonym in the " definiens " the reader is told nothing significantly new ."
12.
He ends his section with the following observation : " A definition may very well rely upon notions that are equivalent to the one being defined; indeed, in every definition " definiens " and " definiendum " are equivalent notions, and the strict observance of Poincar?s demand would make every definition, hence all of science, impossible ".
