432 Dr. St. George Mivart [June 5, 



evidence. It is but the summing uj^, in one general expression, of all 

 the concrete separate cases, such as that of the newt's leg, of the fact 

 that if a man possesses two eyes he cannot at the same time have 

 only one — and so on. 



But an objection has been made as follows : " It is very true that 

 I cannot imagine having two eyes and only one eye at the same 

 time, and so I must practically acquiesce in the statement, but I am 

 only compelled to do so by the impotence of my imagination." Thus 

 instead of the " law of contradiction " Mr. Herbert Spencer has put 

 forward as an ultimate truth his "universal postulate" — the assertion 

 that " we must accept as true propositions we cannot help thinking, 

 because we cannot imagine the contrary." But if any of my hearers 

 will reflect over what his mind tells him when it j^ronounces that he 

 cannot at the same time have both two eyes and only one eye, he will 

 I think, see that his perception is (as mine is) a perception of real 

 incompatibility and consequent positive impossibility. He will not 

 find his mind a mere blank passively unable to imagine something. 

 He will find that his mind actively asserts its power to judge of the 

 matter, as well as what its judgment is, and that the truth is one 

 which positively applies to things and not merely to his own 

 imaginings. 



Moreover, this objection ignores the difference between intellect 

 and imagination. Yet there are very many things we can conceive of 

 but cannot imagine, as for example, our " act of sight " or our own 

 annihilation. But it appears to me evident that Mr. Herbert Spencer's 

 " universal postulate " can never be itself an ultimate truth, but must 

 depend upon the law of contradiction. For, supposing we had tried 

 to imagine a thing and failed, how could we. from that, ever be sure 

 we might not at the same time have tried and succeeded, if we could 

 not rely uj)on the law of contradiction ? The consequences resulting 

 from any real doubt as to this law we will see later on. 



In the pursuit of science, observation is anterior to experiment, 

 but in every observation in which we place confidence, and, still more, 

 in every experiment, a third fundamental truth is necessarily implied : 

 this implied truth is the validity of our faculty of memory. 



It is plain that it would be impossible for us to be certain about 

 any careful observation or any experiment, if we could not feel con- 

 fidence in our memory being able to vouch for the fact that we had 

 observed certain phenomena and what they were. But what is 

 memory ? Evidently we cannot be said to remember anything unless 

 we are conscious that the thing we so remember has been present to 

 our mind on some previous occasion. A mental image might present 

 itself to our imagination a hundred times ; but if at each recurrence 

 it seemed to us something altogether new and unconnected with the 

 past, we could not be said to remember it. It would rather be an 

 example of extreme forgetfulness than of memory. 



By asserting the trustworthiness of our faculty of memory, I do 

 not, of course, mean that we may not occasionally make mistakes 



