This change from Measure to Essential Being is one which Greek philosophy seems to exhibit in the step from Pythagoreanism to Platonism. Plato himself has noted the passage from what have been called the mathematical to the metaphysical categories, and insisted on the essential and higher truth to which mathematics only point. Mathematical terms give the supreme definiteness to the world of being; they show it as in its several compartments a world immanently ordered and measured. As in Greek Art, all seems to be fully brought to the surface: as the image suggests no further and deeper meaning, but affords an absolute identity of aspect and purport; so the natural and semi-popular philosophy of Greece was satisfied for its ethics with the proportionate, the becoming, the beautiful. Plato however passes beyond the surface, and reflects the apparent fact on a deeper permanent reality behind. That reality is still, in name, only the 'form' or 'shape'— only the regular and permanent type—only the measure. But it is called the really real, the ὄντως ὄν,—the being of being. In it the truth is clear, transparent, one and systematic, which in the sensible or immediate world is obscure, confused, multiple. It is the key to explain the difficulties and irregularities of the first and visible scene. Yet even Plato never for a moment forgets the essential correspondence of the two realms, however he may insist upon their separation, and however hard he may find it to explain how being can be duplicated, how the one can be many and yet not cease to be one, how appearance has part in reality.
This indeed is not a difficulty confined to Plato. It is, after all, the same antithesis as we found in the beginning: the Is which lapses into the Is not. It now becomes the play of positive and negative—of perpetual relativity: of a known dependent on an unknown, and an unknown interpreted by a known: an essence guaranteed by its show or seeming and a Schein which supposes permanent Sein. How can a thing be, and yet not be true? How can pleasures seem and not be real? Aristotle, taking up the Platonic antithesis of true and apparent being, carries it on into greater detail. Matter and form: possibility and actuality: are amongst his cardinal pairs of correlatives. But he is anxious to maintain their essential relativity: to show that reality only is and maintains itself as the unity of the two poles of universal and particular, reason and sense, or as a syllogism and a development. So far as he succeeds in doing this, Aristotle rises above the correlational view of reality into the comprehension of it as a unity, which carries itself through difference into self-realisation.
[1] What he did show was that these Ideas were not objects in the vulgar sense of reality, or things.
[2] Cf. the controversy between Schiller and Goethe as to idea and observation, quoted by Whewell, Scientific Ideas, i. 36.
[3] The use of the substantival form Being for the verbal (participle, infinitive, or indicative) suggests an idea of permanence and substance, or essence. So potentiality seems much more real than may or can. And yet the phrase He knows δυνάμει is only equivalent to He can or may know (δύναται or ἐνδέχεται).
[4] When it is said that: 'It is strange that so profound a thinker as Hegel should not have seen that the conception of definite objects, such as a dog and cat, is prior no less in nature than in knowledge to the conception of abstract relations, such as is and is not,' it is difficult to say what the writer meant. Had he ever heard of geometry? Both in nature and in knowledge (i. e. in the natural process from sense to thought) chairs and tables are prior to lines and surface. The mathematical point and line are abstractions, i. e. thoughts, and no image of sensuous reality. It is also true that the ordinary conception of the sun's movements was 'prior no less in nature than in knowledge' to the theory of the earth's rotation. And no doubt Hegel, sedate though his boyhood was, had made the acquaintance of dog and cat in his pre-logical days: as of balls and windows before he was turned upon Euclid. See Mansel's Letters, Lectures, &c., p. 209.
[5] As Being to ordinary unthinkingness seems to mean a great deal it cannot expound, so the mind full of the mystic depths of time and space is disgusted to find them turn so empty and shallow when it would set forth its wealth. See Augustin. Confess. xi. 14.
[6] This may be illustrated by saying that to affirm is the same energy of thought as to deny, and that the difference lies in the terms related by the judgment. In themselves, the one act is as empty or meaningless as the other.
[7] Heine, Ueber Deutschland (Werke), v. 213.