32 LESSONS FROM NATURE. [CHAP. II. 



an internal mental state of conviction, but one less forcible 

 and certain, than the mental state of conviction we have 

 when we say, &quot; whatever thinks, exists.&quot; 



Again, looking into our own mind shows us the strange 

 power it has of seeing a necessary universality in a single 

 experience. Let the three angles of any triangle be once 

 clearly understood to be equal to two right angles, and we 

 also see immediately that in all space, such as the space we 

 know, the three angles within any possible figure bounded by 

 three straight lines must also be equal to two right angles. 



Mr. Lewes indeed tells us * that : &quot; Ideas can be valid only 

 Thought, not as representatives of sensations ;&quot; and from a certain 

 Sof A. point of view this is true, since all our ideas arise 

 through and by means of sensations. But there are ideas 

 which are not and never were representatives of sensation, 

 but of what is or has been suggested to our intellect by 

 means of sensations. Such ideas are, e.g., those of substance, 

 ratio, cause, &c. These ideas when expressed by us in words 

 are deemed and believed, through what we take to be ex 

 perience, to be capable of suggesting to others these similar 

 supra-sensible cognitions, and we think (assuming men like 

 ourselves to exist) that if any one denies this he is not as 

 other men are. 



Mr. Lewes adds : t &quot; All sensation is certain, indisputable. 

 The test and measure of certitude is therefore sensation.&quot; 

 Xow this is bad logic ; such a conclusion would follow only if 

 nothing was certain but sensation. All he can logically con 

 clude is that sensation is &quot; a test and measure of certitude.&quot; 

 In one sense it is such a test not the test. Moreover, it is 

 a test used by the intellect. In feeling itself there is neither 

 certainty nor doubt ; these are the attributes of &quot; thought &quot; 

 only. To say that certitude is in even any one case to be 

 tested by sensation is an incomplete and misleading expression. 

 Certainty, we see by introspection, does not exist at all in 

 feelings, any more than doubt. Both belong to thought only. 



* Problems of Life and Mind, vol. i. p. 181. 

 t Op. cit. p. 257. 



