ONCE the Neo-Platonic period, instead of being left in shadow, is brought into clear historical light, the development of Greek philosophy from Thales to Proclus is seen to consist of two alternations from naturalism to idealism. The "physical" thinkers are followed by Socrates, Plato and Aristotle. Then, by a similar antithesis, the more developed naturalism of the Stoics and Epicureans is followed by the more developed idealism of the Neo-Platonists. The psychology of the Greeks has been brought by Prof. Siebeck under the order assigned by this law. Mr Benn has suggested the law as that of Greek philosophy in general, but without carrying it through in its application to the details. When to the empirical formula the test of psychological deduction is applied, this seems to show that it must have a more general character—that it must be a law, not only of Greek thought, but of the thought of mankind. For evidently, as the objective and subjective points of view become distinguished, the mind must tend to view things first objectively, and then afterwards to make a reflective return on its own processes in knowing. Thus we ought to find universally that a phase of speculative naturalism—the expression of the objective point of view—is followed, when reflection begins to analyse things into appearances for mind, by a phase of idealism. Unfortunately, no exact verification of so extended a deduction can be made out. All that can be said is that the facts do not contradict it.

The law, in the most general terms, may be stated thus: Whenever there is a spontaneous development of philosophic thought beyond the stage of dependence on tradition, a naturalistic phase comes first and an idealistic phase second. In no intrinsic development, whether of individuals or of peoples, is there a reversal of the order. One or other of the phases, however, may be practically suppressed. An individual mind, or the mind of a people, may stop at naturalism, or after the most evanescent phase of it may go straight on to pure idealism. Where both phases definitely appear, as in the case of Greece, we must expect returns of the first, making a repeated rhythm. Further, we must take account of foreign influences, which may modify the intrinsic development. Also, when both stages have been passed through, and are represented by their own teachers, revivals of either may appear at any moment. Thus in modern Europe we can hardly expect to trace through the whole development any law whatever. When thinkers began to break through the new tradition which had substituted itself for ancient mythology and philosophy alike, and had ruled through the Middle Ages, there was from the first a possibility, according to the temper of the individual mind, of reviving any phase of doctrine, naturalistic or idealistic, without respect to its order in the past. We may occasionally get a typical case of the law, as in the idealistic reaction of the Cambridge Platonists on the naturalism of Hobbes; but we cannot expect anything like this uniformly.

Two great ethnical anomalies are the precisely opposite cases of India (that is, of the Hindus) and of China. Nowhere in Asia of course has there been that self-conscious break with traditional authority which we find in ancient Greece and in modern Europe; in both of which cases, however, it must be remembered that the authoritative tradition has never ceased to exist, but has continued always, even in the most sceptical or rational periods, to possess more of direct popular power than philosophy. The philosophies of India and of China are not formally distinct from their religions, and have not found it necessary to repudiate any religious belief simply as such. Still, each has a very distinct character of its own. The official philosophy of China is as purely naturalistic as that of India is idealistic. And in both cases the learned doctrine succeeds in giving a general direction to the mind of the people without appealing to force. With the Hindus, naturalism seems to have been an almost entirely suppressed phase of development. The traces of it found in some of the philosophic systems may be remains of an abortive attempt at a naturalistic view of things in India itself, or may be the result of a foreign influence such as that of Greek Atomism. On the other hand, the Taoism and the Buddhism of China are admittedly much reduced from the elevation they had at first, and have become new elements in popular superstition instead of idealistic philosophies. Buddhism of course is Indian; and Taoism, in its original form perhaps the sole attempt at metaphysics by a native Chinese teacher, seems to have been an indeterminate pantheism, not strictly to be classed either as naturalistic or as idealistic. Both are officially in the shade as compared with Confucianism; and this, while agnostic with regard to metaphysics, is as a philosophy fundamentally naturalistic; adding to ancestral traditions about right conduct simply a very general idea of cosmic order as the theoretic basis for its ethical code.

India and China being thus taken to represent one-sided evolutions of the human mind, we shall see in ancient Greece the normal sequence under a comparatively simplified form. In modern Europe we shall see a complex balance of the two tendencies. Turning from the question of historical law to that of philosophical truth, we may conjecture that the reflective process must somehow mark an advance in insight; but that, if nothing is to be lost, it ought to resume in itself what has gone before. And, as a matter of fact, European idealists, both ancient and modern, have not been content unless they could incorporate objective science with their metaphysics.

Thus we arrive at a kind of "law of three states"—tradition or mythology, naturalism, idealism. In its last two terms, this law seems to be an inversion of the sequence Comte sought to establish from the "metaphysical" to the "positive" stage; naturalism being the philosophy underlying "positivism," while idealism is another name for "metaphysics". How then are we to explain Comte's own mental development? For he undoubtedly held that he himself had passed from tradition through "metaphysics" to "positivity." Exceptio probat regulam: "the exception tests the ruler." In the first place, what Comte regarded as his own metaphysical stage was not metaphysics at all, but a very early mode of political thought in which he accepted from eighteenth century teachers their doctrine of abstract "natural rights." In the second place, his mental history really had a kind of metaphysical phase; but this came after his strictly "positive" or naturalistic period. His later philosophy became subjective on two sides. Having at first regarded mathematics as the sufficient formal basis of all the sciences, he arrived later at the view that before the philosophy of mathematics there ought to be set out a more general statement of principles. That is to say, his intention was to fill up the place that belongs properly to logic, which in its formal division is subjective. Again, in his later scheme, after the highest of the sciences, which he called "morality"—meaning really a psychology of the individual, placed after and not before sociology—there came his "subjective synthesis." This was an adumbration of metaphysics in the true sense of the term; so that his circle of the sciences, beginning with formal principles of reasoning, would have completed itself by running into subjectivity at the other extreme. The apparently exceptional case of Comte therefore turns out to be a real confirmation of the law.

However it may be with this proposed law of three states, there can be no doubt that a very highly developed form of idealism is represented by the Neo-Platonists. How does this stand in relation to modern thought? An obvious position to take up would be to allow the merit of Plotinus and his successors in scientifically elaborating the highest metaphysical conceptions, but to dismiss all their detailed ontology as of merely historic interest. Thus we should fall back upon a position suggested by Plato in the Philebus; namely, that though there may be very little "dialectical," or, as we should now say, metaphysical knowledge, that little may be "pure."

This, however, is too easy a way. The Neo-Platonic thought is, metaphysically, the maturest thought that the European world has seen. Our science, indeed, is more developed; and so also, with regard to some special problems, is our theory of knowledge. On the other hand, the modern time has nothing to show comparable to a continous quest of truth about reality during aperiod of intellectual liberty that lasted for a thousand years. What it has to show, during a much shorter Period of freedom, consists of isolated efforts, bounded by the national limitations of its philosophical schools. The essential ideas, therefore, of the ontology of Plotinus and Proclus may still be worth examining in no merely antiquarian spirit.

A method of examination that suggests itself is to try whether, after all, something of the nature of verification may not be possible in metaphysics. The great defect of idealistic philosophy has been that so little can be deduced from it. The facts of nature do not, indeed, contradict it, but they seem to offer no retrospective confirmation of it. Now this, to judge from the analogy of science, may be owing to the extreme generality with which modern idealism is accustomed to state its positions. It is as if in physics we were reduced to an affirmation of the permanence of "matter" defined in Aristotelian terminology. Let us try what can be made of an idealistic system that undertakes to tell us more than that reality is in some way to be expressed in terms of mind. Plotinus and Proclus, from their theory of being, make deductions that concern the order of phenomena. Since their time, great discoveries have been made in phenomenal science. Do these tend to confirm or to contradict the deductions made from their metaphysical principles by the ancient thinkers?

We must allow, of course, for the defective science of antiquity. The Neo-Platonists cannot be expected to hold any other than the Ptolemaic astronomy. They do not, however, profess to deduce the details of astronomy from their metaphysics. Just as with the moderns, much in the way of detail is regarded as given only by experience. That the universe has this precise constitution—if it has it—is known only as an empirical fact, not as a deduction from the nature of its cause. What the Neo-Platonists deduce metaphysically is not the geocentric system, but the stability of that system—or of any other—if it exists. Thus they do not agree with the Stoics; who, though taking the same view about the present constitution of the universe, held that the system of earth with surrounding planetary and stellar spheres is periodically resolved into the primeval fire and again reconstituted, the resolution being accompanied by an enormous expansion of bulk. All such ideas of an immense total change from a given state of things to its opposite, Plotinus and his successors reject. Any cycle that they can allow involves only changes of distribution in a universe ordered always after the same general fashion. They carry this even into their interpretation of early thinkers like Empedocles. According to Simplicius, the periods of concentration and diffusion which alternate in his cosmogony were by Empedocles himself only assumed hypothetically, and to facilitate scientific analysis and synthesis. For universal intellect, as all the Neo-Platonists say, is ever-existent and produces the cosmic order necessarily; hence it does not sometimes act and sometimes remain in active. Undeviating necessity, in its visible manifestation as in reality, belongs to the divinity above man as to the unconscious nature below him. Change of manifestation depending on apparently arbitrary choice between opposites belongs to man from his intermediate position. To attribute this to the divinity is mythological. There must therefore always be an ordered universe in which every form and grade of being is represented. The phenomenal world, flowing from intellectual being by a process that is necessary and as it were natural, is without temporal beginning or end. These propositions we are already familiar with; and these are the essence of the deduction. Thus if the universe—whatever its detailed constitution may be—does not always as a whole manifest a rational order, the metaphysical principle is fundamentally wrong. To prove scientifically that the world points to an absolute temporal beginning, or that it is running down to an absolute temporal end, or even that it is as a whole alternately a chaos and a cosmos, would be a refutation of the form of idealism held by Plotinus. How then does modern science stand with regard to this position?

It may seem at first sight to contradict it. For does not the theory of cosmic evolution suppose just such immense periodic changes as were conceived by Empedocles, according to the most obvious interpretation of his words? So far as the solar system is concerned, no doubt it does; but the solar system is only a part of the universe. And there seems to be no scientific evidence for the theory that the universe as a whole has periods of evolution and dissolution. Indeed, the evidence points rather against this view. Astronomical observers find existent worlds in all stages. This suggests that, to an observer on any planet, the stellar universe would always present the same general aspect, though never absolute identity of detail as compared with its aspect at any other point of time. For every formed system that undergoes dissolution, some other is evolved from the nebulae which we call relatively "primordial." Thus the total phenomenal manifestation of being remains always the same. If this view should gain strength with longer observation, then science may return in the end to the Neo-Platonic cosmology on an enlarged scale, and again conceive of the whole as one stable order, subject to growth and decay only in its parts. At no time, as the metaphysician will say, is the mind of the universe wholly latent. There is no priority of sense to intellect in the whole. The apparent priority of matter, or of the sentiency of which matter is the phenomenon, is simply an imaginative representation of the evolutionary process in a single system, regarded in isolation from the universe of which it forms part.

That this view is demonstrated by science cannot of course be said. The evidence, however, is quite consistent with it, and seems to point to this rather than to any other of the possible views. The question being not yet scientifically settled, the idealism of Plotinus still offers itself, by the cosmology in which it issues, for verification or disproof. And empirical confirmation, if this were forthcoming, would be quite real as far as it goes, precisely because the metaphysical doctrine is not so very general as to be consistent with all possible facts. A scientific proof that the universe is running down to a state of unalterable fixation would refute it.

To the speculative doctrine of Plotinus no very great addition, as we have seen, was made before Proclus. The additions that Proclus was able to make have by historians as a rule been treated as useless complications,—multiplications of entities without necessity. Yet the power of Proclus as a thinker is not denied even by those who find little to admire in its results; and it had undergone assiduous training. He may be said to have known in detail the whole history of ancient thought, scientific as well as philosophical, at a time when it could still be known without any great recourse to fragments and conjecture. And he came at the end of a perfectly continuous movement. It is therefore of special interest to see how the metaphysical developments he arrived at appear in the light of discoveries made since the European community returned again to the systematic pursuit of knowledge.

What is noteworthy first of all is the way in which, following Aristotle, he has incorporated with the idea of the one stable universe that of an upward movement in the processes that belong to the realm of birth. As we have seen, he distinctly says that in the order of genesis the imperfect comes before the perfect. And this is not meant simply in reference to the individual organism, where it is merely a generalised statement of obvious facts, but is applied on occasion to the history of science. Now the technical terms by which he expresses the philosophical idea of emanation admit of transference to an evolutionary process in time through which its components may be supposed to become explicit. The going forth from the metaphysical principle and the return to it, are not of course themselves processes of the universe in time. Yet there is no reason why they should not have respectively their temporal manifestations in its parts, so long as neither type of manifestation is supposed to be chronologically prior or posterior in relation to the whole. When the terms are thus applied, they find accurate expression in the idea of an evolution, and not of a lapse manifested chronologically,—with which "emanation" is sometimes confounded. Primarily, it is the return to it, rather than thego forth, that becomes manifest as the upward movement. Indeed the term corresponds pretty closely to "involution," which, as Spencer has said, would more truly express the nature of the movement than "evolution." This process is seen in history when thought, by some great discovery, returns to its principle. The antithetic movement, which may be regarded as the manifestation of the return, is seen when, for example, a great discovery is carried, as time goes on, into more and more minute details, or is gradually turned to practical applications. Thus it corresponds to most of what in modern times is called "progress." A corollary drawn by Proclus from his system, it may be noted, also suggests itself from the point of view of modern evolution. The highest and the lowest things, Proclus concludes, are simple; "composition," or complexity, belongs to intermediate natures.

An even more remarkable point of contact between the metaphysics of Proclus and later science is that which presents itself when we bring together his doctrine of the "divine henads " and the larger conceptions of modern astronomy. This doctrine, as we saw, is with Proclus abstract metaphysics. The One, he reasons, must be mediated to the remoter things by many unities, to each of which its own causal "chain" is attached. Elaborate as the theory is, it had, when put forth, hardly any concrete application. If, however, we liberate the metaphysics from the merely empirical part of the cosmology, a large and important application becomes clear. The primal One, as we know, is by Neo-Platonism identified with the Platonic Idea of the Good. Now this, with Plato, corresponds in the intelligible world to the sun in the visible world, and is its cause. But if, as Proclus concluded, the One must be mediated to particular beings by many divine unities, what constitution should we naturally suppose the visible universe to have? Evidently, to each "henad" would correspond a single world which is one of many, each with its own sun. Thus the metaphysical conception of Proclus exactly pre­figures the post-Copernican astronomy, for which each of the fixed stars is the centre of a planetary "chain," and the source of life to the living beings that appear there in the order of birth.

From the infinite potency of the primal Cause, Bruno drew the inference that the universe must consist of actually innumerable worlds. If we take the Neo-Platonic doctrine, not in its most generalised form—in which, as soon as we go beyond a single world, it might seem to issue naturally in an assertion of the quantitative infinite—but with the additions made to it by Proclus, the plurality of worlds certainly becomes more scientifically thinkable. For the "henads" composing, as Proclus says, the plurality nearest to absolute unity—are finite in number. Quantitative infinity he in common with all the school rejects. A kind of infinity of space as a subjective form would have presented no difficulty. Indeed both the geometrical and the arithmetical infinite were allowed by Plotinus in something very like this sense. The difficulty was in the supposition that there are actually existent things in space which are infinite in number. The problem, of course, still remains as one of metaphysical inference. For there can be no astronomical proof either that the whole is finite or that it is infinite. An infinite real ethereal space, with a finite universe of gravitating matter—which seems to be the tacit supposition of those who argue from the fact of radiant heat that the sum of worlds is running down to an end—Bruno and his Neo-Platonic predecessors would alike have rejected.

The Neo-Platonic idealism, it ought now to be evident, was far removed from the reproach of peculiar inability to bring itself into relation with the things of time and space. If both finally baffle the attempt at complete mental comprehension, this, the philosophers would have said, is because they are forms of becoming, and hence remain mixed with illusory imagination. Contrasted with the eternity of intellect, that which appears under those forms is in a sense unreal. The whole philosophy of "genesis," however largely conceived, becomes again what it was for Parmenides, to whom the explanations of physics, though having truth as a coherent order in the world of appearance, where are yet false as compared with the unmixed truth of being. In whatever sense Parmenides conceived of being, the Neo­Platonists, as we know, conceived of it in the manner of idealism. Their idealistic ontology, not deprived of all its detail but merely of its local and temporal features, would, if accepted, clear up more things than the most ambitious of modern systems. That it does not in the end profess to make all things clear, should not be to a modern mind a reason for contemning it, but should rather tell in its favour.