Chapter One
What Can You Really Know?
At five in the afternoon you hear a knock. By the time you reach the door, the corridor is empty. There is a parcel on the mat. You tell your friend, who is waiting inside, that the delivery person has gone. Your friend asks how you know it was a delivery person.
This is an irritating question, which makes it a promising one. You heard a knock and found a parcel. A delivery is the ordinary explanation. You did not see a uniform, a vehicle or a face. A neighbour might have brought the parcel up from a lobby. Your friend might have arranged a surprise and then decided to test your patience. None of these possibilities is likely. But when you said you knew, did you mean there was no other possibility?
The strict answer has a certain beauty. To know is to be beyond error. If another story fits what you observed, you have a reasonable guess, perhaps even a very good belief, but not knowledge. This view protects a word we use with enormous confidence. We ought to reserve that word for cases where the floor cannot give way beneath us.
Let us offer the strict view its chair. If someone told you the parcel contained a fragile gift because they felt sure, you would want to know what they had seen. If they had merely guessed from its size, you might object to the word know. Certainty matters when another person is about to rely on your claim. The desire for a firm boundary between knowledge and confidence is more than pedantry. It is a courtesy to those who must act on what we say.
