Anselm of Canterbury's oeuvre is well known for its reason-centred character, establishing a form of theological thinking that shaped or even initiated scholastics. His main intention was to demonstrate that the content of faith can be understood and argued for intellectually. Anselm's conception of theology as fides quaerens intellectum unfolds itself methodologically in the principle remoto Christo, which forces the acceptance of reason alone as the criterion for knowledge. This leads, as a consequence - in terms of content - to his demonstration of God. A central question is whether it is even possible to find a notion which allows for a description of God's reality and essence. Already his coeval Gaunilo de Marmoutier thematises the limits of thinking, putting in discussion that it is impossible to define God as the unlimited within our intellectual structures and notions. In my contribution, I aim to analyse Anselm's demonstration of God, showing that the structure of his argument does not merely represent a logical deduction intending to develop a notion of God that necessarily includes his existence. In confrontation with the critics of Gaunilo de Marmoutier, I will show that Anselm rather seeks to find a way to express an inner experience in a rational-justified way. By examining at how he argues, I content to argue that he offers a form in which the unsayable, unnameable reality and essence of God can be communicated, not via defining notions but the performativity of thinking as affectus et intellectus.