  When we see two white objects we immediately grasp, “without doubt and deception,” their similarity to one another. Likewise, when we grasp a self-evident truth in our mind, we immediately grasp its truth. Of course, we won’t grasp the truth of the proposition if we don’t understand the meaning of the terms, but in that case we won’t have truly formed the proposition in our mind. And in contrast to the analogous case of recognizing similarity, there is no room for sensory error here. The senses help us acquire certain concepts, but once we have those concepts, the senses drop out of the picture — sensory reliability becomes irrelevant. Scotus offers the example of a blind man miraculously shown in his dreams an image of black and white. Once he acquires these concepts, he can recognize as truly and infallibly as anyone — his blindness notwithstanding — that white is not black (Ord. I.3.1.4 n. 234).