But this very fact points to causes of error so much more dangerous than the mere length of the process, as quite to vitiate the doctrine that the “test of the relative validities of conflicting conclusions” is the number of times the fundamental postulate is involved. On the contrary, the subjects on which the trains of reasoning are longest, and the assumption, therefore, oftenest repeated, are in general those which are best fortified against the really formidable causes of fallacy; as in the example already given of mathematics.
Mr. Spencer makes a distinction between conceiving myself looking into darkness, and conceiving that I am then and there looking into darkness. To me it seems that this change of the expression to the form I am, just marks the transition from conception to belief, and that the phrase “to conceive that I am,” or “that any thing is,” is not consistent with using the word conceive in its rigorous sense.
I have myself accepted the contest, and fought it out on this battle-ground, in the eleventh chapter of An Examination of Sir William Hamilton’s Philosophy.
Chap. xi.
In one of the three cases, Mr. Spencer, to my no small surprise, thinks that the belief of mankind “can not be rightly said to have undergone” the change I allege. Mr. Spencer himself still thinks we are unable to conceive gravitation acting through empty space. “If an astronomer avowed that he could conceive gravitative force as exercised through space absolutely void, my private opinion would be that he mistook the nature of conception. Conception implies representation. Here the elements of the representation are the two bodies and an agency by which either affects the other. To conceive this agency is to represent it in some terms derived from our experiences—that is, from our sensations. As this agency gives us no sensations, we are obliged (if we try to conceive it) to use symbols idealized from our sensations—imponderable units forming a medium.” If Mr. Spencer means that the action of gravitation gives us no sensations, the assertion is one than which I have not seen, in the writings of philosophers, many more startling. What other sensation do we need than the sensation of one body moving toward another? “The elements of the representation” are not two bodies and an “agency,” but two bodies and an effect; viz., the fact of their approaching one another. If we are able to conceive a vacuum, is there any difficulty in conceiving a body falling to the earth through it?
Discussions, etc., 2d ed., p. 624.