 Bob Hale’s (2013, 2021) answer to  (a)  is twofold. He distinguishes between a priori and a posteriori knowledge of essence. In the case of a priori knowledge of essence, essentialist knowledge is based on knowledge of meaning. Hale acknowledges the difference between real and nominal definitions. He then argues that sometimes both a nominal and a real definition of an entity \(x\) can be given by using the same words. For example, Hale argues that knowing the nominal definition of the word “rectangle”, namely knowing the necessary and sufficient conditions for the application of the word, suffices for knowing a priori the real definition or essence of being a rectangle (i.e., a four-sided closed figure consisting of four right angles). 