310 ON SENSATION AND THE UNITY OP 



interpellate: "The upshot of all this long dis- 

 quisition is that we are profoundly ignorant. We 

 knew that to begin with, and you have merely fur- 

 nished another example of the emptiness and use- 

 lessness of metaphysics." But I venture to reply, 

 Pardon me, you were ignorant, but you did not 

 know it. On the contrary, you thought you knew 

 a great deal, and were quite satisfied with the par- 

 ticularly absurd metaphysical notions which you 

 were pleased to call the teachings of common 

 sense. You thought that your sensations were 

 properties of external things, and had an existence 

 outside of yourself. You thought that you knew 

 more about material than you do about immaterial 

 existences. And if, as a wise man has assured us, 

 the knowledge of what we don't know is the next 

 best thing to the knowledge of what we do know, 

 this brief excursion into the province of philos- 

 ophy has been highly profitable. 



Of all the dangerous mental habits, that which 

 schoolboys call " cocksureness " is probably the 

 most perilous; and the inestimable value of 

 metaphysical discipline is that it furnishes an 

 effectual counterpoise to this evil proclivity. 

 Whoso has mastered the elements of philosophy 

 knows that the attribute of unquestionable cer- 

 tainty appertains only to the existence of a state 

 of consciousness so long as it exists; all other 

 beliefs are mere probabilities of a higher or lower 

 order. Sound metaphysic is an amulet which 



