XLIV. (181) And that is not the least influential cause of the instability of one’s perceptions which arises from the position of the objects, from their distance, and from the places by which they are each of them surrounded. (182) Do we not see that the fishes in the sea, when they stretch out their fins and swim about, do always appear larger than their real natural size? And oars too, even though they are very straight, look as if they were broken when they are under water; and things at a great distance display false appearances to our eyes, and in this way do frequently deceive the mind. (183) For at times inanimate objects have been imagined to be alive, and on the contrary living animals have been considered to be lifeless; sometimes again stationary things appear to be in motion, and things in motion appear to be standing still: even things which are approaching towards us do sometimes appear to be retreating from us, and things which are going away do on the other hand appear to be approaching. At times very short things seem to be exceedingly long, and things which have many angles appear to be circular. There is also an infinite number of other things of which a false impression is given though they are open to the sight, which however no man in his senses would subscribe to as certain.

XLV. (184) What again are we to say of the quantities occurring in things compounded? For it is through the admixture of a greater or a lesser quantity that great injury or good is often done, as in many other instances, so most especially in the case of medicines compounded by medical science. (185) For quantity in such compounds is measured by fixed limits and rules, and it is not safe either to stop short before one has reached them, nor to advance beyond them. For if too little be applied, it relaxes, and if too much, it strains the natural powers; and each extremity is mischievous, the one from its impotence being capable of producing any effect at all, and the other by reason of its exceeding strength being necessarily hurtful. Again it is very plain with reference to smoothness, and roughness, and thickness, and close compression, or on the other hand leanness and slackness, how very much influence all these differences have in respect of doing good or harm. (186) Nor indeed is any one ignorant that scarcely anything whatever of existing things, if you consider it in itself and by itself, is accurately understood; but by comparing it with its opposite, then we arrive at a knowledge of its true nature. As for instance, we comprehend what is meant by little by placing it in juxta-position with what is great; we understand what dry is by comparing it with wet, cold by comparing it with heat, light by comparing it with heavy, black by contrasting it with white, weak by contrasting it with strong, and few by comparing it with many. In the same way also, in whatever is referred to virtue or to vice, (187) what is advantageous is recognised by a comparison with what is injurious, what is beautiful by a comparison with what is unseemly, what is just and generally good, by placing it in juxta-position with what is unjust and bad. And, indeed, if any one considers everything that there is in the world, he will be able to arrive at a proper estimate of its character, by taking it in the same manner; for each separate thing is by itself incomprehensible, but by a comparison with another thing, is easy to understand it. (188) Now, that which is unable to bear witness to itself, but which stands in need of the advocacy of something else, is not to be trusted or thought steady. So that in this way those men are convicted who say that they have no difficulty in assenting to or denying propositions about anything. (189) And why need we wonder? For any one who advances far into matters, and who contemplates them in an unmixed state will know this, that nothing is ever presented to our view according to its real plain nature, but that everything has the most various possible mixtures and combinations.