158 



REASONING. 



they no doubt found it as impossible 

 to conceive that a body should act 

 upon the earth from the distance of 

 the siin or moon, as we find it to con- 

 ceive an end to space or time, or two 

 straight lines enclosing a space. 

 Newton himself had not been able 

 to realise the conception, or we should 

 not have had his hypothesis of a 

 subtle ether, the occult cause of gra- 

 vitation ; and his writings prove, that 

 though he deemed the particular 

 nature of the intermediate agency a 

 matter of conjecture, the necessity of 

 some such agency appeared to him 

 indubitable. 



If, then, it be so natural to the 

 human mind, even in a high state of 

 culture, to be incapable of conceiving, 

 and on that ground to believe impos- 

 sible, what is afterwards not only 

 found to be conceivable but proved to 

 be true ; what wonder if in cases 

 where the association is still older, 

 more confirmed, and more familiar, 

 and in which nothing ever occurs to 

 shake our conviction, or even suggest 

 to us any conception at variance with 

 the association, the acquired incapa- 

 city should continue, and be mistaken 

 for a natural incapacity ? It is true, 

 our experience of the varieties in 

 nature enables us, within certain 

 limits, to conceive other varieties 

 analogous to them. We can conceive 

 the sun or moon falling ; for though 

 we never saw them fall, nor ever 

 perhaps imagined them falling, we 

 have seen so many other things fall, 

 that we have innumerable familiar 

 analogies to assist the conception ; 

 which, after all, we should probably 



in a letter to the Abb6 Conti, "par la nature 

 des creatures est miraculeui. II ne sufl&t 

 pas de dire : Dieu a fait une telle loi de 

 nature ; done la chose est uaturelle. II 

 faut que la loi soit executable par les na- 

 tures des creatures. Si Dieu donnait cette 

 loi. par exemple, k un coips libre, de 

 tourner k I'entour d'un certain centre, il 

 faudrait ou qu'il y joignlt d'autres corps qui 

 par leur impulsion i'obligeassent de renter 

 toujours dans son orbite circulaire, ou qu'il 

 mU un ange d ses trousses, ou evfin il faudrait 

 qu'il y concourUt extraordinairement ; car 

 naturellement il s'^cartera par latangente." 

 '^ Works of Leibnitz, ed. Dutens, iii. 446. 



have some difficulty in framing, were 

 we not well accustomed to see the sun 

 and moon move, (or appear to move,) 

 so that we are only called upon to 

 conceive a slight change in the direc- 

 tion of motion, a circumstance familiar 

 to our experience. But when experi- 

 ence affords no model on which to 

 shape the new conception, how is it 

 possible for us to form it ? How, for 

 example, can we imagine an end to 

 space or time ? We never saw any 

 object without something beyond it, 

 nor experienced any feeling without 

 something following it. When, there- 

 fore, we attempt to conceive the last 

 point of space, we have the idea 

 irresistibly raised of other points be- 

 yond it. When we try to imagine 

 the last instant of time, we cannot 

 help conceiving another instant after 

 it. Nor is there any necessity to 

 assume, as is done by a modern 

 school of metaphysicians, a peculiar 

 fundamental law of the mind to 

 account for the feeling of infinity 

 inherent in our conceptions of space 

 and time ; that apparent infinity is 

 sufficiently accounted for by simpler 

 and universally acknowledged laws. 



Now, in the case of a geometrical 

 axiom, such, for example, as that two 

 straight lines cannot enclose a space, 

 — a truth which is testified to us by 

 our very earliest impressions of the 

 external world, — how is it possible 

 (whether those external impressions 

 be or be not the ground of our belief) 

 that the reverse of the proposition 

 could be otherwise than inconceivable 

 to us ? What analogy have we, what 

 similar order of facts in any other 

 branch of our experience, to facilitate 

 to us the conception of two straight 

 lines enclosing a space ? Nor is even 

 this all. I have already called atten- 

 tion to the peculiar property of our 

 impressions of form, that the ide»,s or 

 mental images exactly resemble their 

 prototypes, and adequately represent 

 them for the purposes of scientific 

 observation. From this, and from the 

 intuitive character of the observation, 

 which in this case reduces itself to 



