His major work, De Docta Ignorantia (‘Of Learned Ignorance’, 1440) espouses a ‘negative theology’, in which a Neoplatonic conception of the cosmos renders its nature entirely unknowable. He is also associated with the doctrine of the ‘concordance of contraries’, an attack on the Aristotelian law of non-contradiction which was historically influential. In cosmology he was one of the earliest thinkers to deny the geocentric theory of the universe, and to affirm the unbounded nature of space.