Intuitionistic Fuzzy Sets Theory is based on a wrong nominalistic (terminological) assumption. It is defined as “intuitionistic” a negation which does not satisfy usual properties of the intuitionistic Brouwer negation, but it is called with this term only a particular generalized notion of negation which indeed corresponds to the de Morgan negation. This metatheoretical assumption is criticized and the role of different generalized negations is discussed.