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I may call them by a general name ; for instance, Grounds of 

 Scientific Necessity ; and these are precisely what I mean by 

 Fundamental Ideas. 



That some steady thought, and even some progress 

 in the construction of Science, is needed in order to see 

 the necessity of the Axioms thus introduced, is true, and is 

 repeatedly asserted and illustrated in the History of the 

 Sciences. The necessity of such Axioms is seen, but it is 

 not seen at first. It becomes clearer and clearer to each 

 person, and clear to one person after another, as the human 

 mind dwells more and more steadily on the several subjects 

 of speculation. There are scientific truths which are seen by 

 intuition, but this intuition is progressive. This is the remark 

 which I wish to make in answer to those of my critics who 

 have objected that truths which I have propounded as Axioms, 

 are not -evident to all. 



That the Axioms of Science are not evident to all, is true 

 enough, and too true. Take the Axiom of Substance : fohat 

 we may change the condition of a substance in various ways, 

 but cannot destroy it. This has been assumed as evident by 

 philosophers in all ages ; but if we ask an ordinary person 

 whether a body can be destroyed by fire, or diminished, will 

 he unhesitatingly reply, that it cannot? It requires some 

 thought to say, as the philosopher said, that the weight of 

 the smoke is to be found by subtracting the weight of the 

 ashes from that of the fuel ; nay, even when this is said, it 

 appears at, first, rather an epigram than a scientific truth. 

 Yet it is by thinking only, not by an experiment, that, from 

 a happy guess it becomes a scientific truth. And the thought 

 is the basis, not the result, of experimental truths ; for which 

 reason I ascribe it to a Fundamental Idea. And so, such 

 truths are the genuine growth of the human mind ; not 

 innate, as if they needed not to grow ; still less, dead 

 twigs plucked from experience and stuck in from without ; 



