As an example, imagine someone took you to a strange building. You’re standing at the closed front door, and that person asks you, “What’s behind that door, inside the building?” How much could you know through reason? You might be able to guess some things, like perhaps there being tables and chairs and lights and taps...but you could be wrong. It could be completely empty or completelyfull, or...well, almost anything. So how could you know, how could you reach certainty about what is behind that door? Well, of course you could go in and see it with your own eyes, but what if that was not possible? How, then, could you come to know what is inside?