Passing by now the fact that Plato has furnished no satisfactory proof for the objective and independent reality of ideas, and that his theory is without vindication, we may affirm in the first place that it is wholly unfruitful, since it possesses no ground of explanation for being. The ideas have no proper and independent content. To see this we need only refer to the manner in which Plato introduced them. In order to make science possible he had posited certain substances independent of the sensible, and uninfluenced by its changes. But to serve such a purpose, there was offered to him nothing other than this individual thing of sense. Hence he gave to this individual a universal form, which was with him the idea. From this it resulted, that his ideas can hardly be separated from the sensible and individual objects which participate in them. The ideal duality and the empirical duality is one and the same content. The truth of this we can readily see, whenever we gain from the adherents to the doctrine of ideas a definite statement respecting the peculiar character of their unchangeable substances, in comparison with the sensible and individual things which participate in them. The only difference between the two consists in appending per se to the names expressing the respective ideas; thus, while the individual things are e. g. man, horse, etc., the ideas are man per se, horse per se, etc. There is only this formal change for the doctrine of ideas to rest upon; the finite content is not removed, but is only characterized as perpetual. This objection, that in the doctrine of ideas we have in reality only the sensible posited as a not-sensible, and endowed with the predicate of immutability, Aristotle urges as above remarked when he calls the ideas “immortalized things of sense,” not as though they were actually something sensible and spacial, but because in them the sensible individual loses at once its individuality, and becomes a universal. He compares them in this respect with the gods of the popular and anthropomorphical religion; as these are nothing but deified men, so the ideas are only things of nature endowed with a supernatural potency, a sensible exalted to a not-sensible. This identity between the ideas and their respective individual things amounts moreover to this, that the introduction of ideas doubles the objects to be known in a burdensome manner, and without any good results. Why set up the same thing over again? Why besides the sensible twofoldness and threefoldness, affirm a twofoldness and threefoldness in the idea? The adherents of the doctrine of ideas, when they posit an idea for every class of natural things, and through this theory set up two equivalent theories of sensible and not-sensible substances, seem therefore to Aristotle like men who think they can reckon better with many numbers than with few, and who therefore go to multiplying their numbers before they begin their reckoning. Therefore again the doctrine of ideas is a tautology, and wholly unfruitful of the explanation of being, “The ideas give no aid to the knowledge of the individual things participating in them, since the ideas are not immanent in these things, but separate from them.” Equally unfruitful are the ideas when considered in reference to the arising and departing of the things of sense. They contain no principle of becoming, of movement. There is in them no causality which might bring out the event, or explain the event when it had actually happened. Themselves without motion and process, if they had any effect, it could only be that of perfect repose. True, Plato affirms in his Phædon that the ideas are causes both of being and becoming, but in spite of the ideas, nothing ever becomes without a moving; the ideas, by their separation from the becoming, have no such capacity to move. This indifferent relation of ideas to the actual becoming, Aristotle brings under the categories, potentiality and actuality, and farther says that the ideas are only potential, they are only bare possibility and essentiality because they are wanting in actuality.—The inner contradiction of the doctrine of ideas is in brief this, viz., that it posits an individual immediately as a universal, and at the same time pronounces the universal, the species, as numerically an individual, and also that the ideas are set up on the one side as separate individual substances, and on the other side as participant, and therefore as universal. Although the ideas as the original conceptions of species are a universal, which arise when being is fixed in existence, and the one brought out in the many, and the abiding is given a place in the changeable, yet can they not be defined as they should be according to the Platonic notion, that they are individual substances, for there can be neither definition nor derivation of an absolute individual, since even the word (and only in words is a definition possible) is in its nature a universal, and belongs also to other objects, consequently, every predicate in which I attempt to determine an individual thing cannot belong exclusively to that thing. The adherents of the doctrine of ideas, are therefore not at all in a condition to give an idea a conceivable termination; their ideas are indefinable.—In general, Plato has left the relation of the individual objects to ideas very obscure. He calls the ideas archetypes, and allows that the objects may participate in them; yet are these only poetical metaphors. How shall we represent to ourselves this “participation,” this copying of the original archetype? We seek in vain for more accurate explanations of this in Plato. It is impossible to conceive how and why matter participates in the ideas. In order to explain this, we must add to the ideas a still higher and wider principle, which contains the cause for this “participation” of objects, for without a moving principle we find no ground for “participation.” Alike above the idea (e. g. the idea of man), and the phenomenon (e. g. the individual man), there must stand a third common to both, and in which the two were united, i. e. as Aristotle was in the habit of expressing this objection, the doctrine of ideas leads to the adoption of a “third man.” The result of this Aristotelian criticism is the immanence of the universal in the individual. The method of Socrates in trying to find the universal as the essence of the individual, and to give definitions according to conception, was as correct (for no science is possible without the universal) as the theory of Plato in exalting these universal conceptions to an independent subsistence as real individual substances, was erroneous. Nothing universal, nothing which is a kind or a species, exists besides and separate from the individual; a thing and its conception cannot be separated from each other. With these principles Aristotle hardly deviated from Plato’s fundamental idea that the universal is the only true being, and the essence of individual things; it may rather be said that he has freed this idea from its original abstraction, and given it a more profound mediation with the phenomenal world. Notwithstanding his apparent contradiction to Plato, the fundamental position of Aristotle is the same as that of his master, viz., that the essence of a thing (τὸ τί ἐστιν, τὸ τί ἦν εἶναι) is known and represented in the conception; Aristotle however recognizes the universal, the conception to be as little separated from the determined phenomenon as form from matter, and essence or substance (οὐσία) in its most proper sense is, according to him, only that which cannot be predicated of another, though of this other every remaining thing may be predicated; it is that which is a this (τόδε τι), the individual thing and not a universal.
(2.) The four Aristotelian principles or causes, and the relation of form and matter.—From the criticism of the Platonic doctrine of ideas arose directly the groundwork of the Aristotelian system, the determinations of matter (ὕλη), and form (εἶδος). Aristotle enumerates four metaphysical principles or causes: matter, form, moving cause, and end. In a house, for instance, the matter is the wood, the form is the conception of the house, the moving cause is the builder, and the end is the actual house. These four determinations of all being resolve themselves upon a closer scrutiny into the fundamental antithesis of matter and form. The conception of the moving cause is involved with the two other ideal principles of form and of end. The moving cause is that which has secured the transition of the incomplete actuality or potentiality to the complete actuality, or induces the becoming of matter to form. But in every movement of the incomplete to the complete, the latter antedates in conception this movement, and is its motive. The moving cause of matter is therefore form. So is man the moving and producing cause of man; the form of the statue in the understanding of the artist is the cause of the movement by which the statue is produced; health must be in the thought of the physician before it can become the moving cause of convalescence; so in a certain degree is medicine, health, and the art of building the form of the house. But in the same way, the moving or first cause is also identical with the final cause or end, for the end is the motive for all becoming and movement. The moving cause of the house is the builder, but the moving cause of the builder is the end to be attained, i. e. the house. From such examples as these it is seen that the determinations of form and end may be considered under one, in so far as both are united in the conception of actuality (ἐνέργεια), for the end of every thing is its completed being, its conception or its form, the bringing out into complete actuality that which was potentially contained in it. The end of the hand is its conception, the end of the seed is the tree, which is at the same time the essence of the seed. The only fundamental determinations, therefore, which cannot be wholly resolved into each other, are matter and form.
Matter when abstracted from form in thought, Aristotle regarded as that which was entirely without predicate, determination and distinction. It is that abiding thing which lies at the basis of all becoming; but which in its own being is different from every thing which has become. It is capable of the widest diversity of forms, but is itself without determinate form; it is every thing in possibility, but nothing in actuality. There is a first matter which lies at the basis of every determinate thing, precisely as the wood is related to the bench and the marble to the statue. With this conception of matter Aristotle prides himself upon having conquered the difficulty so frequently urged of explaining the possibility that any thing can become, since being can neither come out of being nor out of not-being. For it is not out of not-being absolutely, but only out of that which as to actuality is not-being, but which potentially is being, that any thing becomes. Possible or potential being is no more not-being than actuality. Every existing object of nature is hence but a potential thing which has become actualized. Matter is thus a far more positive substratum with Aristotle than with Plato, who had treated it as absolutely not-being. From this is clearly seen how Aristotle could apprehend matter in opposition to form as something positively negative and antithetic to the form, and as its positive denial (στέρησις).
As matter coalesces with potentiality, so does form coincide with actuality. It is that which makes a distinguishable and actual object, a this (τόδε τι) out of the undistinguished and in determinate matter; it is the peculiar virtue, the completed activity, the soul of every thing. That which Aristotle calls form, therefore, is not to be confounded with what we perhaps may call shape; a hand severed from the arm, for instance, has still the outward shape of a hand, but according to the Aristotelian apprehension, it is only a hand now as to matter and not as to form: an actual hand, a hand as to form, is only that which can do the proper work of a hand. Pure form is that which, in truth, is without matter (τὸ τί ἦν εἶναι); or, in other words, the conception of being, the pure conception. But such pure form does not exist in the realm of determined being; every determined being, every individual substance (οὐσία), every thing which is a this, is rather a totality of matter and form, a (σύνολον). It is, therefore, owing to matter, that being is not pure form and pure conception; matter is the ground of the becoming, the manifold, and the accidental; and it is this, also, which gives to science its limits. For in precisely the measure in which the individual thing bears in itself a material element is it uncognizable. From what has been said, it follows that the opposition between matter and form is a variable one, that being matter in one respect which in another is form; building-wood, e. g. is matter in relation to the completed house, but in relation to the unhewn tree it is form; the soul in respect to the body is form, but in respect to the reason, which is the form of form (εἶδος εἴδους) is it matter. On this standpoint the totality of all existence may be represented as a ladder, whose lowest step is a prime matter (πρώτη ὕλη), which is not at all form, and whose highest step is an ultimate form which is not at all matter, but is pure form (the absolute, divine spirit). That which stands between these two points is in one respect matter, and in another respect form, i. e. the former is ever translating itself into the latter. This position, which lies at the basis of the Aristotelian view of nature, is attained analytically through the observation that all nature exhibits the perpetual and progressive transition of matter into form, and shows the exhaustless and original ground of things as it comes to view in ever ascending ideal formations. That all matter should become form, and all that is potential should be actual, and all that is should be known, is doubtless the demand of the reason and the end of all becoming; yet is this actually impracticable, since Aristotle expressly affirms that matter as the antithesis, or denial of form, can never become wholly actualized, and therefore can never be perfectly known. The Aristotelian system ends thus like its predecessors, in the unsubdued dualism of matter and form.
(3.) Potentiality and Actuality (δύναμις and ἐνέργεια).—The relation of matter to form, logically apprehended, is but the relation of potentiality to actuality. These terms, which Aristotle first employed according to their philosophical significance, are very characteristic for his system. We have in the movement of potential being to actual being the explicit conception of becoming, and in the four principles we have a distribution of this conception in its parts. The Aristotelian system is consequently a system of the becoming, in which the Heraclitic principle appears again in a richer and profounder apprehension, as that of the Eleatics had done with Plato. Aristotle in this has made no insignificant step towards the subjection of the Platonic dualism. If matter is the possibility of form, or reason becoming, then is the opposition between the idea and the phenomenal world potentially overcome, at least in principle, since there is one being which appears both in matter and form only in different stages of development. The relation of the potential to the actual Aristotle exhibits by the relation of the unfinished to the finished work, of the unemployed carpenter to the one at work upon his building, of the individual asleep to him awake. Potentially the seed-corn is the tree, but the grown up tree is it actually; the potential philosopher is he who is not at this moment in a philosophizing condition; even before the battle the better general is the potential conqueror; potentially is space infinitely divisible; in fact every thing is potentially which possesses a principle of motion, of development, or of change, and which, if unhindered by any thing external, will be of itself. Actuality or entelechy on the other hand indicates the perfect act, the end as gained, the completely actual (the grown-up tree e.g. is the entelechy of the seed-corn), that activity in which the act and the completeness of the act fall together, e. g. to see, to think where he sees and he has seen, he thinks and he has thought (the acting and the completeness of the act) are one and the same, while in those activities which involve a becoming, e. g. to learn, to go, to become well, the two are separated. In this apprehension of form (or idea) as actuality or entelechy, i. e. in joining it with the movement of the becoming, is found the chief antagonism of the Aristotelian and Platonic systems. Plato considers the idea as being at rest, and consisting for itself, in opposition to the becoming and to motion; but with Aristotle the idea is the eternal product of the becoming, it is an eternal energy, i. e. an activity in complete actuality, it is not perfect being, but is being produced in every moment and eternally, through the movement of the potential to its actual end.
(4.) The Absolute, Divine Spirit.—Aristotle has sought to establish from a number of sides, the conception of the absolute spirit, or as he calls it, the first mover, and especially by joining it to the relation of potentiality and actuality.
(a.) The Cosmological Form.—The actual is ever antecedent to the potential not only in conception (for I can speak of potentiality only in reference to some activity) but also in time, for the acting becomes actual only through an acting; the uneducated becomes educated through the educated, and this leads to the claim of a first mover which shall be pure activity. Or, again, it is only possible that there should be motion, becoming, or a chain of causes, except as a principle of motion, a mover exists. But this principle of motion must be one whose essence is actuality, since that which only exists in possibility cannot alone become actual, and therefore cannot be a principle of motion. All becoming postulates with itself that which is eternal and which has not become, that which itself unmoved is a principle of motion, a first mover.
(b.) The Ontological Form.—In the same way it follows from the conception of potentiality, that the eternal and necessary being cannot be potential. For that which potentially is, may just as well either be or not be; but that which possibly is not, is temporal and not eternal. Nothing therefore which is absolutely permanent, is potential, but only actual. Or, again, if potentiality be the first, then can there be no possible existence, but this contradicts the conception of the absolute or that which it is impossible should not be.
(c.) The Moral Form.—Potentiality always involves a possibility to the most opposite. He who has the capacity to be well, has also the capacity to be sick, but actually no man is at the same time both sick and well. Therefore actuality is better than potentiality, and only it can belong to the eternal.
(d.) So far as the relation of potentiality and actuality is identical with the relation of matter and form, we may apprehend in the following way these arguments for the existence of a being which is pure actuality. The supposition of an absolute matter without form (the πρώτη ὕλη) involves also the supposition of an absolute form without matter (a πρῶτον εἶδος). And since the conception of form resolves itself into the three determinations, of the moving, the conceivable, and the final cause, so is the eternal one the absolute principle of motion (the first mover πρῶτον χινοῦν), the absolute conception or pure intelligible (the pure τί ἧν εἶναι) , and the absolute end.