Sells, M.A. :
Mystical Languages of Unsaying, 
University of Chicago Press - Chicago, 1994, p.21, italics mine.

 "When Plotinus writes that 'it is neither X not not X', he violates the logical rule of the excluded middle. When he writes that 'it is both X and not X' he violates the law of noncontradiction. (...) Real contradictions arise when the delimited, referential function of language encounters a rigorously apophatic notion of the unlimited. (...) Each proposition taken alone is self-contradictory, analytically incoherent. Meaning is generated between two propositions : it is within all things - it is beyond all things. In effect, the smallest semantic unity is not the sentence or proposition, but the double sentence or dual proposition. It is to this new semantic of the double proposition that apophatic dialectical logic applies."