The Square Root of Minus One, No. 6, 1988, is part of Joseph Kosuth’s series of works on the writings of Siegmund Freund, the silkscreen lettering quoting from Sigmund Freud’s essay ‘Negation’ (1925) “I should like to take this into me and to keep that out of me” on the glass panel, the philosophical term “monás” is printed in Greek lettering on the wall, combined with a metal plate showing underlined the title The Square Root of Minus One and below the sign for square root ‘√-1’. “Monad” (from Greek ‘monás’, unit, and ‘monos’, alone), according to the Pythagoreans, was a term for God or the first being, or the totality of all beings, “Monad” being the source or the One meaning without division. In Kosuth’s visual constellation and circular interdependence of mathematical, philosophical and psycholo-gical concepts, the straightforward mathematical proposition supports quite a different reading: Here three intellectual or scientific definitions of the idea of ‘unity’ open up a conversation.