Plato and the Other Companions of Sokrates, 3rd ed. Volume 1

In what manner Diodorus stated and defended his opinion upon this point, we have no information. We know only that he placed affirmations respecting the future on the same footing as affirmations respecting the past: maintaining that our potential affirmation — May or May not be — respecting some future event, meant no more than it means respecting some past event, viz.: no inherent indeterminateness in the future sequence, but our ignorance of the determining conditions, and our inability to calculate their combined working.66 In regard to scientific method generally, this problem is of the highest importance: for it is only so far as uniformity of sequence prevails, that facts become fit matter for scientific study.67 Consistently with the doctrine of all-pervading uniformity of sequence, the definition of Hobbes gives the only complete account of the Impossible and Possible: i.e. an account such as would appear to an omniscient calculator, where May or May not merge in Will or Will not. According as each person falls short of or approaches this ideal standard — according to his knowledge and mental resource, inductive and deductive — will be his appreciation of what may be or may not be — as of what may have been or may not have been during the past. But such appreciation, being relative to each individual mind, is liable to vary indefinitely, and does not admit of being embodied in one general definition.

Besides the above doctrine respecting Possible and Impossible, there is also ascribed to Diodorus a doctrine respecting Hypothetical Propositions, which, as far as I comprehend it, appears to have been a correct one.68 He is also said to have reasoned against the reality of motion, renewing the arguments of Zeno the Eleate.

But if he reproduced the arguments of Zeno, he also employed another, peculiar to himself. He admitted the reality of past motion: but he denied the reality of present motion. You may affirm truly (he said) that a thing has been moved: but you cannot truly affirm that any thing is being moved. Since it was here before, and is there now, you may be sure that it has been moved: but actual present motion you cannot perceive or prove. Affirmation in the perfect tense may be true, when affirmation in the present tense neither is nor ever was true: thus it is true to say — Helen had three husbands (Menelaus, Paris, Deiphobus): but it was never true to say — Helen has three husbands, since they became her husbands in succession.69 Diodorus supported this paradox by some ingenious arguments, and the opinion which he denied seems to have presented itself to him as involving the position of indivisible minima — atoms of body, points of space, instants of time. He admitted such minima of atoms, but not of space or time: and without such admission he could not make intelligible to himself the fact of present or actual motion. He could find no present Now or Minimum of Time; without which neither could any present motion be found. Plato in the Parmenidês70 professes to have found this inexplicable moment of transition, but he describes it in terms not likely to satisfy a dialectical mind: and Aristotle denying that the Now is any portion or constituent part of time, considers it only as a boundary of the past and future.71

This opinion of Aristotle is in the main consonant with that of Diodorus; who, when he denied the reality of present motion, meant probably only to deny the reality of present motion apart from past and future motion. Herein also we find him agreeing with Hobbes, who denies the same in clearer language.72 Sextus Empiricus declares Diodorus to have been inconsistent in admitting past motion while he denied present motion.73 But this seems not more inconsistent than the doctrine of Aristotle respecting the Now of time. I know, when I compare a child or a young tree with what they respectively were a year ago, that they have grown: but whether they actually are growing, at every moment of the intervening time, is not ascertainable by sense, and is a matter of probable inference only.74 Diodorus could not understand present motion, except in conjunction with past and future motion, as being the common limit of the two: but he could understand past motion, without reference to present or future. He could not state to himself a satisfactory theory respecting the beginning of motion: as we may see by his reasonings distinguishing the motion of a body all at once in its integrity, from the motion of a body considered as proceeding from the separate motion of its constituent atoms — the moving atoms preponderating over the atoms at rest, and determining them to motion,75 until gradually the whole body came to move.

That Diodorus was a person seriously anxious to solve logical difficulties, as well as to propose them, would be incontestably proved if we could believe the story recounted of him — that he hanged himself because he could not solve a problem proposed by Stilpon in the presence of Ptolemy Soter.77 But this story probably grew out of the fact, that Stilpon succeeded Diodorus at Megara, and eclipsed him in reputation. The celebrity of Stilpon, both at Megara and at Athens (between 320-300 B.C., but his exact date can hardly be settled), was equal, if not superior, to that of any contemporary philosopher. He was visited by listeners from all parts of Greece, and he drew away pupils from the most renowned teachers of the day; from Theophrastus as well as the others.78 He was no less remarkable for fertility of invention than for neatness of expression. Two persons, who came for the purpose of refuting him, are said to have remained with him as admirers and scholars. All Greece seemed as it were looking towards him, and inclining towards the Megaric doctrines.79 He was much esteemed both by Ptolemy Soter and by Demetrius Poliorkêtes, though he refused the presents and invitations of both: and there is reason to believe that his reputation in his own day must have equalled that of either Plato or Aristotle in theirs. He was formidable in disputation; but the nine dialogues which he composed and published are characterised by Diogenes as cold.80

Contemporary with Stilpon (or perhaps somewhat later) was Menedêmus of Eretria, whose philosophic parentage is traced to Phædon. The name of Phædon has been immortalised, not by his own works, but by the splendid dialogue of which Plato has made him the reciter. He is said (though I doubt the fact) to have been a native of Elis. He was of good parentage, a youthful companion of Sokrates in the last years of his life.81 After the death of Sokrates, Phædon went to Elis, composed some dialogues, and established a succession or sect of philosophers — Pleistanus, Anchipylus, Moschus. Of this sect Menedêmus,82 contemporary and hearer of Stilpon, became the most eminent representative, and from him it was denominated Eretriac instead of Eleian. The Eretriacs, as well as the Megarics, took up the negative arm of philosophy, and were eminent as puzzlers and controversialists.

But though this was the common character of the two, in a logical point of view, yet in Stilpon, as well as Menedêmus, other elements became blended with the logical. These persons combined, in part at least, the free censorial speech of Antisthenes with the subtlety of Eukleides. What we hear of Menedêmus is chiefly his bitter, stinging sarcasms, and clever repartees. He did not, like the Cynic Diogenes, live in contented poverty, but occupied a prominent place (seemingly under the patronage of Antigonus and Demetrius) in the government of his native city Eretria. Nevertheless he is hardly less celebrated than Diogenes for open speaking of his mind, and carelessness of giving offence to others.83