proof, it is certainly necessary that the proof be true, or he will be untrustworthy. Now will he say that the proof which he has accepted for the accrediting of the criterion is true, having judged it, or without having judged it? If he says so 116 without judging it, he will be untrustworthy; if he has judged it, it is evident that he will say that he has judged according to some criterion, and we must seek a proof for this criterion, and for that proof a criterion. For the proof always needs a criterion to establish it, and the criterion needs a proof that it may be shown to be true; and a proof can neither be sound without a pre-existing criterion that is true, nor a criterion true without a proof that is shown beforehand to be trustworthy. And so both the criterion and the proof are thrown into the 117 _circulus in probando_, by which it is found that they are both of them untrustworthy, for as each looks for proof from the other, each is as untrustworthy as the other. Since then one cannot prefer one idea to another, either without a proof and a criterion or with them, the ideas that differ according to different conditions cannot be judged, so that the suspension of judgment in regard to the nature of external objects follows through this Trope also. THE FIFTH TROPE. The fifth Trope is that based upon position, distance, and 118 place, for, according to each of these, the same things appear different, as for example, the same arcade seen from either end appears curtailed, but from the middle it looks symmetrical on every side; and the same ship appears small and motionless from afar, and large and in motion near by, and the same tower appears round from a distance, but square near by. So much for distance. Now in reference to place, we say that the light 119 of the lamp appears dim in the sun, but bright in the dark; and the same rudder appears broken in the sea, but straight out of it; and the egg in the bird is soft, but in the air hard; and the lyngurion is a fluid in the lynx, but is hard in the air; and the coral is soft in the sea, but hard in the air; and a tone of voice appears different produced by a syrinx, and by a flute, and different simply in the air. Also in reference to 120 position, the same picture leaned back appears smooth, and leaned forward a little seems to have hollows and protuberances, and the necks of doves appear different in color according to the difference in inclination. Since then all phenomena are 121 seen in relation to place, distance, and position, each of which relation makes a great difference with the idea, as we have mentioned, we shall be obliged by this Trope also to come to the suspension of judgment. For he who wishes to give preference to certain ones of these ideas will attempt the impossible. For if 122 he simply makes the decision without proof he will be untrustworthy. If, however, he wishes to make use of a proof,