OPAQUENESS. Implicit in Descartes' cogito, ergo sum one finds an assumption about the transparency of the mind: through a universal doubt one will be able to obtain a "clear mind" that can provide a proper foundation of knowledge. Locke conceptualised the mind as initially being a tabula rasa, an idea which is also associated to the notion of transparency.60 And as already emphasised, Brentano' protophenomenology and Husserl's phenomenology included assumptions about transparency of the mind.