Brains know reality through a combination of perception and inference to the best explanation of what is observed. Such inference attempts to maximize explanatory coherence, which sometimes requires rejection of what the senses tell us. Rejection of observations occurs both in everyday life, as when a drunk decides that a double image of a person cannot be right, and in science, as when a researcher throws out some experimental data that conflict with a well-supported theory. Hence gaining knowledge is a matter of seeking coherence among many hypotheses and pieces of evidence, not of starting with some indubitable foundation in sense experience or a priori knowledge and trying to base everything else on that.