332 THE FOUNDATIONS OF ZOOLOGY 



actions for the attainment of ends ? May not some of the things 

 we see and feel be illusions ? He who is giddy feels the world 

 turn round. One who has lost his legs may suffer from cold feet. 

 We see the sun rise in the morning and run his course through 

 the sky until the evening. From the windows of the moving 

 train we see the ranks of corn circle round the middle distance. 

 The skilful dramatist makes us feel all the emotions and impulses 

 a real tragedy would excite. 



While all the things we see and feel are, no doubt, equally 

 real, they are not all real in the same way ; for while it is true 

 that we cannot doubt the evidence of our senses, familiar experi- 

 ence teaches that our senses are often deceptive, since their evi- 

 dence stands in need of continual correction ; for delusion and 

 hallucination and error are, unfortunately, as real as truth. 



The most practical and important question which rational living 

 beings can ask is how we may distinguish truth from error, in 

 order that we may think wisely, and be sure about our actions, 

 and rightly order our lives ; and the greatest service of Charles 

 Darwin to the intellectual life of mankind is that he has led us 

 to ask whether we may not some time find a mechanical explana- 

 tion of that rational judgment which is innate in intelligent human 

 beings ; whether this may not itself be part of the physical 

 order of nature ; whether language itself, even the most rational 

 discourse, may not be a natural phenomenon, which lies entirely 

 within the limits of physical causation; whether proof that nature 

 is a language is proof that this language is supernatural. 



He asks whether those judgments which we call errors may 

 not be the ones which lead us into danger and tend to our physi- 

 cal destruction, and whether it may not be because a judgment has 

 proved beneficial in the struggle for existence that we call it true. 



On the other hand, he does not forget that hallucinations, 

 even those of the insane, are themselves truths of nature, which, 

 wisely interpreted, may help the physician to minister to a mind 

 diseased. He therefore asks whether hallucinations are not use- 

 ful in the same way that all natural knowledge is useful ; whether 

 illusions and errors are not truths misunderstood ; whether they 

 are exceptions to the rule that all natural knowledge is useful 

 and instructive to all who hear aright the language of nature. 



