Lives and Opinions of Eminent Philosophers

"For those who are unable, Herodotus, to examine thoroughly each detail of what we have written concerning nature, nor to study through the larger treatises composed by us, I have myself prepared an epitome of the whole system, so that they may sufficiently retain in memory the most general doctrines, in order that on each occasion they may be able to help themselves in the most principal matters, to the extent that they apply themselves to the study of nature. And those too who have made sufficient progress in the survey of the whole must remember the elementary outline of the entire system; for we have frequent need of the comprehensive grasp, but not similarly of the detailed one.

"One must, then, continually proceed to those detailed matters as well, but in memory one must retain just so much as will afford the most principal grasp of things, and indeed through which all the detailed accuracy will be discovered, once the most general outlines are well apprehended and remembered; since even for the fully accomplished thinker this becomes the most principal part of all exact knowledge: to be able to make swift use of intuitive grasps, with each matter being brought back to simple elementary principles and terms. For it is impossible to know the compact fabric of the continuous survey of the whole if one is unable to comprehend within oneself, through brief utterances, everything that could also be thoroughly examined in detail.

"Whence, since such a path is useful to all who are familiar with natural science—recommending continuous activity in natural science, and finding peace of mind especially in such a life—I have composed for you as well such an epitome and elementary exposition of the whole of the doctrines. "First of all, then, Herodotus, one must grasp the things subordinated to utterances, in order that we may have that to which we can refer our opinions, inquiries, or difficulties and thereby judge them, and that everything may not go on unjudged for us who demonstrate to infinity, or that we may not hold empty utterances.

​For it is necessary that the primary concept corresponding to each utterance be seen and need no demonstration, if we are to have that to which we will refer the thing sought, doubted, or opined. Furthermore, one must keep watch over all sensations, and simply the immediate grasps whether of the intellect or of any of the criteria whatsoever, and likewise the existing feelings, in order that we may have that by which we can infer both what awaits confirmation and what is non-evident. "Having distinguished these points, we must now view comprehensively what concerns non-evident matters. First, that nothing comes into being from what does not exist. For everything would come into being from everything, standing in need of no seeds whatsoever.

​And if that which disappears were destroyed into non-existence, all things would have perished, since there would be nothing into which they dissolved. Furthermore, the universe was always such as it now is, and always will be such. For there is nothing into which it will change; for besides the universe there is nothing which, entering into it, could produce the change. "Moreover—〔this he also states at the beginning of the Large Epitome and in Book 1 of On Nature〕—the universe consists of bodies and void. For that bodies exist, sensation itself testifies in all cases, according to which it is necessary to make inference with reasoning concerning the non-evident;

​and if there were not that which we call void, space, and intangible nature, bodies would not have where to be, nor through what to move, just as they are seen to move. But beyond these nothing can even be conceived, either comprehensively or by analogy with things comprehensively grasped, being taken as complete natures and not being spoken of as accidents or properties of these. "Moreover, of bodies—〔this too is in the first book of On Nature, and in the fourteenth and fifteenth, and in the Large Epitome〕—some are compounds, and others are those from which the compounds have been made.