624 FALLACIES. 



vei'um esse ;" whatever can be very clearly conceived must certainly exist ; 

 that is, as he afterward explains it, if the idea includes existence. And on 

 this ground he infers that geometrical figures really exist, because they 

 can be distinctly conceived. Whenever existence is " involved in an idea," 

 a thing conformable to the idea must really exist; which is as much as to 

 say, whatever the idea contains must have its equivalent in the thing ; and 

 what we are not able to leave out of the idea can not be absent from the 

 reality.* This assumption pervades the philosophy not only of Descartes, 

 but of all the thinkers who received their impulse mainly from him, in par- 

 ticular the two most remarkable among them, Spinoza and Leibnitz, from 

 whom the modern German metaphysical philosophy is essentially an ema- 

 nation. I am indeed disposed to think that the fallacy now under consid- 

 eration has been the cause of two-thirds of the bad philosophy, and espe- 

 cially of the bad metaphysics, which the human mind has never ceased to 

 produce. Our general ideas contain nothing but what has been put into 

 them, either by our passive experience, or by our active habits of thought; 

 and the metaphysicians in all ages, who have attempted to construct the 

 laws of the universe by reasoning from our supposed necessities of thought, 

 have always proceeded, and only could proceed, by laboriously finding in 

 their own minds what they themselves had formerly put there, and evolv- 

 ing from their ideas of things what they had first involved in those ideas. 

 In this Avay all deeply-rooted opinions and feelings are enabled to create 

 apparent demonstrations of their truth and reasonableness, as it were, out 

 of their own substance. 



The other form of the fallacy: Things which we can not think of to- 

 gether can not exist togethei" — including as one of its branches, that what 

 we can not think of as existing can not exist at all — may thus be briefly 

 expressed : Whatever is inconceivable must be false. 



Against this prevalent doctrine I have sufiiciently argued in a former 

 Book,f and nothing is required in this place but examples. It was long 

 held that Antipodes were impossible because of the difliculty which was 

 found in conceiving persons with their heads in the same direction as our 

 feet. And it was one of the received arguments against the Copernican 

 system, that we can not conceive so great a void space as that system sup- 

 poses to exist in the celestial regions. When men's imaginations had al- 

 ways been used to conceive the stars as firmly set in solid spheres, they 

 naturally found much difficulty in imagining them in so different, and, as 

 it doubtless appeared to them, so precarious a situation. But they had no 

 right to mistake the limitation (whether natural, or, as it in fact proved, 

 only artificial) of their own faculties, for an inherent limitation of the pos- 

 sible modes of existence in the universe. 



It may be said in objection, that the error in these cases was in the 

 minor premise, not the major; an error of fact, not of principle; that it 

 did not consist in supposing that what is inconceivable can not be true, but 



* The author of one of the Bridgewater Treatises has fallen, as it seems to me, into a simi- 

 lar fallacy when, after arguing in rather a curious way to prove that matter may exist with- 

 out any of the known properties of matter, and may therefore be changeable, he concludes 

 that it can not be eternal, because "etenial (passive) existence necessarily involves incapa- 

 bility of change." I believe it would be difficult to point out any other connection between 

 the facts of eternity and unchangeableness, than a strong association between the two ideas. 

 Most of the a priori arguments, both religious and anti-religious, on the origin of things, are 

 fallacies drawn from the same source. 



t Supra, book ii., chap, v., § 6, and chap, vii., § 1, 2, 3, 4. See also Examination of Sir 

 William Hamilton's Philosophy, chap. vi. and elsewhere. 



