that there is any material substance.  But if by material substance is meant only sensible body, that which is seen and felt (and the unphilosophical part of the world, I dare say, mean no more)—­then I am more certain of matter’s existence than you or any other philosopher pretend to be.  If there be anything which makes the generality of mankind averse from the notions I espouse, it is a misapprehension that I deny the reality of sensible things.  But, as it is you who are guilty of that, and not I, it follows that in truth their aversion is against your notions and not mine.  I do therefore assert that I am as certain as of my own being, that there are bodies or corporeal substances (meaning the things I perceive by my senses); and that, granting this, the bulk of mankind will take no thought about, nor think themselves at all concerned in the fate of those unknown natures, and philosophical quiddities, which some men are so fond of.

HYL.  What say you to this?  Since, according to you, men judge of the reality of things by their senses, how can a man be mistaken in thinking the moon a plain lucid surface, about a foot in diameter; or a square tower, seen at a distance, round; or an oar, with one end in the water, crooked?

Phil.  He is not mistaken with regard to the ideas he actually perceives, but in the inference he makes from his present perceptions.  Thus, in the case of the oar, what he immediately perceives by sight is certainly crooked; and so far he is in the right.  But if he thence conclude that upon taking the oar out of the water he shall perceive the same crookedness; or that it would affect his touch as crooked things are wont to do:  in that he is mistaken.  In like manner, if he shall conclude from what he perceives in one station, that, in case he advances towards the moon or tower, he should still be affected with the like ideas, he is mistaken.  But his mistake lies not in what he perceives immediately, and at present, (it being a manifest contradiction to suppose he should err in respect of that) but in the wrong judgment he makes concerning the ideas he apprehends to be connected with those immediately perceived:  or, concerning the ideas that, from what he perceives at present, he imagines would be perceived in other circumstances.  The case is the same with regard to the Copernican system.  We do not here perceive any motion of the earth:  but it were erroneous thence to conclude, that, in case we were placed at as great a distance from that as we are now from the other planets, we should not then perceive its motion.

HYL.  I understand you; and must needs own you say things plausible enough.  But, give me leave to put you in mind of one thing.  Pray, Philonous, were you not formerly as positive that Matter existed, as you are now that it does not?

Phil.  I was.  But here lies the difference.  Before, my positiveness was founded, without examination, upon prejudice; but now, after inquiry, upon evidence.