THEORIES CONCERNING AXIOMS. 299 



ceive that one body could produce motion in another without 

 contact. They had as much experience of other modes of pro- 

 ducing motion, as they had of that mode. The planets had 

 revolved, and heavy bodies had fallen, every hour of their lives. 

 But they fancied these phenomena to be produced by a hidden 

 machinery which they did not see, because without it they 

 were unable to conceive what they did see. The inconceiv- 

 ableness, instead of representing their experience, dominated 

 and overrode their experience. It is needless to dwell farther 

 on what I have termed the positive argument of Mr. Spencer 

 in support of his criterion of truth. I pass to his negative 

 argument, on which he lays more stress. 



3. The negative argument is, that, whether inconceiv- 

 ability be good evidence or bad, no stronger evidence is to be 

 obtained. That what is inconceivable cannot be true, is pos- 

 tulated in every act of thought. It is the foundation of all our 

 original premises. Still more it is assumed in all conclusions 

 from those premises. The invariability of belief, tested by the 

 inconceivableness of its negation, "is our sole warrant for 

 every demonstration. Logic is simply a systematization of 

 the process by which we indirectly obtain this warrant for 

 beliefs that do not directly possess it. To gain the strongest 

 conviction possible respecting any complex fact, we either 

 analytically descend from it by successive steps, each of which 

 we unconsciously test by the inconceivableness of its negation, 

 until we reach some axiom or truth which we have similarly 

 tested ; or we synthetically ascend from such axiom or truth 

 by such steps. In either case we connect some isolated belief, 

 with a belief which invariably exists, by a series of interme- 

 diate beliefs which invariably exist." The following passage 

 sums up the whole theory : " When we perceive that the 

 negation of the belief is inconceivable, we have all possible 

 warrant for asserting the invariability of its existence : and in 

 asserting this, we express alike our logical justification of it, 

 and the inexorable necessity we are under of holding it. . . ; 

 We have seen that this is the assumption on which every con- 

 clusion whatever ultimately rests. We have no other guarau- 



