1891.] on the Implications of Science. 437 



ago, are tnown to us only in roundabout ways, and we often feel 

 more or less want of certainty about them. On the other hand we 

 have a practical certainty concerning the things which are about us 

 at any given moment. Thus we have come to associate a feeling of 

 uncertainty with statements about things very remote. But nothing 

 can well be more remote from us than the more distant regions of 

 space or before the origin of the solar system. It is not surprising 

 then that this mental association should call forth a feeling of un- 

 certainty with respect to any statement about universal truth. 



It is no doubt wonderful that we should be able to know any 

 necessary and universal truths; but it is less exceptionally wonderful, 

 when we come to think the matter all round, than it may at first 

 sight appear to be. It is wonderful, but so, deeply considered, is all 

 our knowledge. It is wonderful that through molecular vibrations, 

 or other occult powers of bodies, we have sensations — ^such as of 

 musical tones, sweetness, blueness, or what not. It is wonderful 

 that through sensations, actual and remembered, we have perceptions. 

 It is wonderful that on the occurrence of certain perceptions, we 

 recognise our own existence past and present. So also it is wonderful 

 that we recognise that what we know is, cannot at the same time not 

 be. The fact is so, and we perceive it to be so ; we know things and 

 we know that we know them. How we know them is a mystery 

 indeed, but one about which it is, I think, perfectly idle to speculate. 

 It is precisely parallel to the mystery of sensation. We feel things 

 savoury or odorous, or brilliant, or melodious, as the case may be ; 

 and with the aid of the scalpel and the microscope we may investigate 

 the material conditions of such sensations. But how such conditions 

 can give rise to the feelings themselves, is a mystery which defies 

 our utmost efforts to penetrate. I make no pretension to be able to 

 throw any light upon the problem How is knowledge possible ? 

 any more than on the problem How is sensation possible? or on the 

 questions How is life possible ? or How is extension possible ? but 

 " Ignorantia modi non tollit certitudinem facti " ; and we know that 

 we are living, that we feel, and that we do know something — if only 

 that we know we doubt about the certainty of our knowledge. 



And, with respect to such doubt, let me here put before you the 

 intellectual penalties which have to be paid for any real and serious 

 doubt with respect to the implications of science. I think we shall 

 see that nothing less than intellectual suicide or mental paralysis 

 must be the result. And such a result must also be logically fatal 

 to every branch of science. 



The first implication I put before you was the validity of infer- 

 ence. Now no one who argues, or who listens to or reads, with any 

 serious intention, the arguments of others, can, without stultifying 

 himself, profess to think that no process of reasoning is valid. If 

 the truth of no mode of reasoning is certain, if we can make no 

 certain inferences at all, then all arguments must be useless, and to 

 proffer, or to consider, them must be alike vain. But not only must 



Vol. XIII. (No. 85.) 2 g 



