co-operation in an effective copula is, if that be possible, further aggravated. His grasp of the problem, if we may judge from the relatively small body of documentary evidence, was not so sure as that of Empedocles, though he employed in general the same means for its solution. He too postulates a mixture of all substances, more consciously and definitely indeed than his predecessor. Believing that only like can act on like,97 he is led to assume not only an infinite multiplicity of substances, but also their complete mixture, so that everything, however small, contains a portion of every other. Food, for example, however seeming-simple, nourishes the most diverse tissues of the body. Thus we discover in the universal mixture of substances the basis for co-operation and interaction.
Anaxagoras, therefore, like Empedocles, feels the need of bridging the chasm which he has assumed to exist between his distinct substances. Their failure is alike great, and is due to the presuppositions they inherited from the Eleatic conception of a severe homogeneity which implies an absolute difference from everything else. The embarrassment of Anaxagoras increases with the introduction of the Νοῦς. This agency was conceived with a view to explaining the formation of the world; that is, with a view to mediating between the myriad substances in their essential aloofness and effecting the harmonious concord of concrete things. While, even on the basis of a universal mixture, the function of the Νοῦς was foredoomed to failure, its task was made more difficult still by the definition given to its nature. According to Anaxagoras it was the sole exception to the composite character of things; it is absolutely pure and simple in nature.98 By its definition, then, it is prevented from accomplishing the work it was contrived to do; and hence we cannot be surprised at the lamentations raised by Plato and Aristotle about the failure of Anaxagoras to employ the agency he had introduced. To be sure, the Νοῦς is no more a deus ex machina than were the ideas of Plato or the God of Aristotle. They all labored under the same restrictions.
The Atomists followed with the same recognition of the Many, in the infinitely various kinds of atoms; but it was tempered by the assumption of an essential homogeneity. One atom is distinguished from another by characteristics due to its spatial relations. Mass and weight are proportional to size. Aristotle reports that, though things and atoms have differences, it is not in virtue of their differences, but in virtue of their essential identity, that they interact.99 There is thus introduced a distinction which runs nearly, but not quite, parallel to that between primary and secondary qualities.100 Primary qualities are those of size, shape, and perhaps101 position; all others are secondary. On the other hand, that which is common to all atoms is their corporeity, which does indeed define itself with reference to the primary (spatial) qualities, but not alike in all. The atoms of which the world is constituted are alike in essential nature, but they differ most widely in position.
It is the void that breaks up the unity of the world—atomizes it, if we may use the expression. It is the basis of all discontinuity. Atoms and void are thus polar extremes reciprocally exclusive. The atoms in their utter isolation in space are incapable of producing a world. In order to bridge the chasm between atom and atom, recourse is had to motion eternal, omnipresent, and necessary. This it is that annihilates distances. In the course of their motion atoms collide, and in their impact one upon the other the Atomists find the precise mode of co-operation by which the world is formed.102 To this agency are due what Lucretius happily called "generating motions."
The problem, however, so insistently pursued the philosophers of this time that the Atomists did not content themselves with this solution, satisfactory as modern science has pretended to consider it. They followed the lead of Empedocles and Anaxagoras in postulating a widespread, if not absolutely universal, mixture. Having on principle excluded "essential" differences among the atoms, the impossibility of finally distinguishing essential and non-essential had its revenge. Important as the device of mixture was to Empedocles and Anaxagoras, just so unmeaning ought it to have been in the Atomic philosophy, provided that the hypothesis could accomplish what was claimed for it. It is not necessary to reassert that the assumption of "individua," utterly alienated one from the other by a void, rendered the problem of the copula insoluble for the Atomists.
Diogenes of Apollonia is commonly treated contemptuously as a mere reactionary who harked back to Anaximenes and had no significance of his own. The best that can be said of such an attitude is that it regards philosophical theories as accidental utterances of individuals, naturally well or ill endowed, who happen to express conclusions with which men in after times agree or disagree. A philosophical tenet is an atom, set somewhere in a vacuum, utterly out of relation to everything else. But it is impossible to see how, on this theory, any system of thought should possess any significance for anybody, or how there should be any progress even, or retardation.
Viewed entirely from without, the doctrine of Diogenes would seem to be substantially a recrudescence of that of Anaximenes. Air is once more the element or ἀρχή out of which all proceeds and into which all returns. Again the process of transformation is seen in rarefaction and condensation; and the attributes of substance are those which were common to the early hylozoists. But there is present a keen sense of a problem unknown to Anaximenes. What the early philosopher asserted in the innocence of the youth of thought, the later physiologist reiterates with emphasis because he believes that the words are words of life.
The motive for recurring to the earlier system is supplied by the imperious demand for a copula which had so much distressed Empedocles, Anaxagoras, and the Atomists. And here we are not left to conjecture, but are able to refer to the ipsissima verba of our philosopher. After a brief prologue, in which he stated that one's starting-point must be beyond dispute, he immediately103 turned to his theme in these words:104 "In my opinion, to put the whole matter in a nutshell, all things are derived by alteration from the same substance, and indeed all are one and the same. And this is altogether evident. For if the things that now exist in the world—earth and water and air and fire and whatsoever else appears to exist in this world—if, I say, any one of these were different from the other, different that is to say in its proper peculiar nature, and did not rather, being one and the same, change and alter in many ways, then in no-wise would things be able to mix with one another, nor would help or harm come to one from the other, nor would any plant spring from the earth, nor any other living thing come into being, if things were not so constituted as to be one and the same."
These words contain a singularly interesting expression of the need of restoring the integrity of the process which had been lost in the effort to solve the problem of the One and the Many without abandoning the point of view won by the Eleatics. Aristotle and Theophrastus paraphrase and sum up the passage above quoted by saying105 that interaction is impossible except on the assumption that all the world is one and the same. Hence it is manifest, as was said above, that the return of Diogenes to the monistic system of Anaximenes had for its conscious motive the avoidance of the dualism that had sprung up in the interval and had rendered futile the multiplied efforts to secure an effective copula.
We should note, however, that in the attempt thus made to undo the work of several generations Diogenes retained the principle which had wrought the mischief. We have before remarked that the germ of the Atomic philosophy was contained in the process of rarefaction and condensation. Hence, in accepting it along with the remainder of Anaximenes's theory, the fatal assumption was reinstated. It is the story of human systems in epitome. The superstructure is overthrown, and with the débris a new edifice is built upon the old foundations.
In the entire course of philosophical thought from Thales onward the suggestion of an opposition between the subject and the predicate had appeared. It has often been said that it was expressed by the search for a φύσις, or a true nature, in contrast with the world as practically accepted. There is a certain truth in this view; for the effort to attain a predicate which does not merely repeat the subject does imply that there is an opposition. But the efforts made to return from the predicate to the subject, in a deductive movement, shows that the difference was not believed to be absolute. This is true, however, only of those fields of speculation that lie next to the highways of practical life, which lead equally in both directions, or, let us rather say, which unite while they mark separation. In the sphere of abstract ideas the sense of embarrassment was deep and constantly growing deeper. The reconstruction, accomplished on lower levels, did not attain unto those heights. Men doubted conclusions, but did