the witness of our feeble sight.’  It must be admitted that this observation is correct, and although it be true that the appearance of roundness comes simply from the effacement of the angles, which distance causes to disappear, it is true, notwithstanding, that the round and the square are opposites.  Therefore my answer to this objection is that the representation of the senses, even when they do all that in them lies, is often contrary to the truth; but it is not the same with the faculty of reasoning, when it does its duty, since a strictly reasoned argument is nothing but a linking together of truths.  And as for the sense of sight in particular, it is well to consider that there are yet other false appearances which come not from the ‘feebleness of our eyes’ nor from the loss of visibility brought about by distance, but from the very nature of vision, however perfect it be.  It is thus, for instance, that the circle seen sideways is changed into that kind of oval which among geometricians is known as an ellipse, and sometimes even into a parabola or a hyperbola, or actually into a straight line, witness the ring of Saturn.

65.  The external senses, properly speaking, do not deceive us.  It is our inner sense which often makes us go too fast.  That occurs also in brute beasts, as when a dog barks at his reflexion in the mirror:  for beasts have consecutions of perception which resemble reasoning, and which occur also in the inner sense of men, when their actions have only an empirical quality.  But beasts do nothing which compels us to believe that they have what deserves to be properly called a reasoning sense, as I have shown elsewhere.  Now when the understanding uses and follows the false decision of the inner sense (as when the famous Galileo thought that Saturn had[110] two handles) it is deceived by the judgement it makes upon the effect of appearances, and it infers from them more than they imply.  For the appearances of the senses do not promise us absolutely the truth of things, any more than dreams do.  It is we who deceive ourselves by the use we make of them, that is, by our consecutions.  Indeed we allow ourselves to be deluded by probable arguments, and we are inclined to think that phenomena such as we have found linked together often are so always.  Thus, as it happens usually that that which appears without angles has none, we readily believe it to be always thus.  Such an error is pardonable, and sometimes inevitable, when it is necessary to act promptly and choose that which appearances recommend; but when we have the leisure and the time to collect our thoughts, we are in fault if we take for certain that which is not so.  It is therefore true that appearances are often contrary to truth, but our reasoning never is when it proceeds strictly in accordance with the rules of the art of reasoning.  If by reason one meant generally the faculty of reasoning whether well or ill, I confess that it might deceive us, and does indeed deceive us, and the appearances of our understanding are often as deceptive as those of the senses:  but here it is a question of the linking together of truths and of objections in due form, and in this sense it is impossible for reason to deceive us.