Thought or Intelligence — was produced by influx of atoms from without.
As sensation, so also thought or intelligence, was produced by the working of atoms from without. But in what manner the different figures and magnitudes of atoms were understood to act, in producing diverse modifications of thought, we do not find explained. It was, however, requisite that there should be a symmetry, or correspondence of condition between the thinking mind within and the inflowing atoms from without, in order that these latter might work upon a man properly: if he were too hot, or too cold, his mind went astray.[236] Though Demokritus identified the mental or vital particles with the spherical atoms constituting heat or fire, he nevertheless seems to have held that these particles might be in excess as well as in deficiency, and that they required, as a condition of sound mind, to be diluted or attempered with others. The soundest mind, however, did not work by itself or spontaneously, but was put in action by atoms or effluvia from without: this was true of the intellectual mind, not less than of the sensational mind. There was an objective something without, corresponding to and generating every different thought — just as there was an objective something corresponding to every different sensation. But first, the object of sensation was an atomic compound having some appreciable bulk, while that of thought might be separate atoms or vacua so minute as to be invisible and intangible. Next, the object of sensation did not reveal itself as it was in its own nature, but merely produced changes in the percipient, and different changes in different percipients (except as to heavy and light, hard and soft, which were not simply modifications of our sensibility, but were also primary qualities inherent in the objects themselves[237]): while the object of thought, though it worked a change in the thinking subject, yet also revealed itself as it was, and worked alike upon all.
[236] Theophrast. De Sensu, 58. Περὶ δὲ τοῦ φρονεῖν ἐπὶ τοσοῦτον εἴρηκεν, ὅτι γίνεται συμμέτρως ἐχούσης τῆς ψυχῆς μετὰ τὴν κίνησιν· ἐὰν δὲ περίθερμός τις ἢ περίψυχρος γένηται, μεταλλάττειν φησί.
[237] Theophrastus, De Sensu, 71. νῦν δὲ σκληροῦ μὲν καὶ μαλακοῦ καὶ βαρέος καὶ κούφου ποιεῖ τὴν οὐσίαν, ὅπερ (ἅπερ) οὐχ’ ἧττον ἔδοξε λέγεσθαι πρὸς ἡμᾶς, θερμοῦ δὲ καὶ ψυχροῦ καὶ τῶν ἄλλων οὐδενός.
This is a remarkable point to be noted in the criticisms of Theophrastus on the doctrine of Demokritus. Demokritus maintains that hot and cold are relative to us: hard and soft, heavy and light, are not only relative to us, but also absolute, objective, things in their own nature, — though causing in us sensations which are like them. Theophrastus denies this distinction altogether: and denies it with the best reason. Not many of his criticisms on Demokritus are so just and pertinent as this one.
Sensation, obscure knowledge relative to the sentient; Thought, genuine knowledge — absolute, or object per se.
Hence Demokritus termed sensation, obscure knowledge — thought, genuine knowledge.[238] It was only by thought (reason, intelligence) that the fundamental realities of nature, atoms and vacua, could be apprehended: even by thought, however, only imperfectly, since there was always more or less of subjective movements and conditions, which partially clouded the pure objective apprehension — and since the atoms themselves were in perpetual movement, as well as inseparably mingled one with another. Under such obstructions, Demokritus proclaimed that no clear or certain knowledge was attainable: that the sensible objects, which men believed to be absolute realities, were only phenomenal and relative to us, — while the atoms and vacua, the true existences or things in themselves, could scarce ever be known as they were:[239] that truth was hidden in an abyss, and out of our reach.
[238] Demokritus Fragm. Mullach, p. 205, 206; ap. Sext. Empir. adv. Mathemat. vii. 135-139, γνώμης δύο εἰσὶν ἰδέαι· ἡ μὲν γνησίη, ἡ δὲ σκοτίη, &c.
[239] Democr. Frag., Mull., p. 204-5. Ἅπερ νομίζεται μὲν εἶναι καὶ δοξάζεται τὰ αἰσθητά, οὐκ ἔστι δὲ κατὰ ἀλήθειαν ταῦτα· ἀλλὰ τὰ ἄτομα μόνον καὶ κενόν. ἡμέες δὲ τῷ μὲν ἐόντι οὐδὲν ἀτρεκὲς ξυνίεμεν, μετάπιπτον δὲ κατά τε σώματος διαθιγήν, καὶ τῶν ἐπεισιόντων, καὶ τῶν ἀντιστηριζόντων … ἐτεῇ μέν νυν, ὅτι οἵον ἕκαστόν ἐστιν ἢ οὔκ ἐστιν, οὐ ξυνίεμεν, πολλαχῆ δεδήλωται, &c.
Compare Cicero, Acad. Quæst. i. 13, ii. 10; Diog. Laert. ix. 72; Aristotel. Metaphys. iii. 5, p. 1009, b. 10.