 If I want to understand the substance of a square white wall, I turn my mind away from thinking about whiteness, and quantity, and shape, and location, and when it was built, and all the other individual circumstances connected with the wall, every one of which I had recognised beforehand, either by means of my external senses, or conceived earlier abstractly in my imagination, and I draw forth cognition of something I have never perceived sensorily, namely, the subject of these things. (AM: I.445) 