This was more than evident to Pascal (in a fragment from 1655): "One cannot begin to define being without falling victim to this absurdity: one cannot define a word without beginning with the term is, be it expressly stated or merely understood. To define being, therefore, you have to say is, thus using the term to be defined in the definition." Which is not the same as saying, as Gorgias said, that we cannot speak of being: we speak about it all the time, too often perhaps; the problem is that this magic word helps us define almost everything but is defined by nothing.
In semantics we would speak of a primitive, the most primitive of all.#6264•