Dr. Henry More has also a passage asserting the essential correlation on which I am here insisting (Immortality of the Soul, ch. ii. p. 3). And Professor Ferrier, in his Institutes of Metaphysic, has given much valuable elucidation respecting the essential relativity of cognition.
Though this note is already long, I shall venture to add from an eminent German critic — Trendelenburg — a passage which goes to the same point.
“Das Sein ist als die absolute Position erklärt worden. Der Begriff des Seins drücke blos das aus: es werde bei dem einfachen Setzen eines Was sein Bewenden haben. Es hat sich hier die abstracte Vorstellung des Seins nur in eine verwandte Anschauung umgekleidet; denn das Gesetzte steht in dem Raum da; und insofern fordert die absolute Position schon den Begriff des seiendem Etwas, das gesetzt wird. Fragt man weiter, so ist in der absoluten Position schon derjenige mitgedacht, der da setzt. Das Sein wird also nicht unabhängig aus sich selbst bestimmt, sondern zur Erklärung ein Verhältniss zu der Thätigkeit des Gedankens herbeigezogen.
“Aehnlich würde jede von vorn herein versuchte Bestimmung des Denkens ausfallen. Man würde es nur durch einen Bezug zu den Dingen erläutern können, welche in dem Denken Grund und Mass finden. Wir begeben uns daher jeder Erklärung, und setzen eine Vorstellung des Denkens und Seins voraus, in der Hoffnung dass beide mit jedem Schritt der Untersuchung sich in sich selbst bestimmen werden.” “Indem wir Denken und Sein unterscheiden, fragen wir, wie ist es möglich, dass sich im Erkennen Denken und Sein vereinigt? Diese Vereinigung sprechen wir vorläufig als eine Thatsache aus, die das Theoretische wie das Praktische beherrscht.” Trendelenburg, Logische Untersuchungen, sect. 3, pp. 103-104, Berlin, 1840.
Object always relative to Subject — Either without the other, impossible. Plato admits this in Sophistes.
I cannot therefore agree with Plato in regarding the Protagorean doctrine — Homo Mensura — as having any dependance upon, or any necessary connection with, the other theory (canvassed in the Theætêtus) which pronounces cognition to be sensible perception. Objects of thought exist in relation to a thinking Subject; as Objects of sight or touch exist in relation to a seeing or touching Subject. And this we shall find Plato himself declaring in the Sophistes (where his Eleatic disputant is introduced as impugning a doctrine substantially the same as that of Plato himself in the Phædon, Timæus, and elsewhere) as well as here in the Theætêtus. In the Sophistes, certain philosophers (called the Friends of Forms or Ideas) are noticed, who admitted that all sensible or perceivable existence (γένεσις — Fientia) was relative to a (capable) sentient or percipient — but denied the relativity of Ideas, and maintained that Ideas, Concepts, Intelligible Entia, were not relative but absolute. The Eleate combats these philosophers, and establishes against them — That the Cogitable or Intelligible existence, Ens Rationis, was just as much relative to an Intelligent or Cogitant subject, as perceivable existence was relative to a Subject capable of perceiving — That Existence, under both varieties, was nothing more than a potentiality, correlating with a counter-potentiality (τὸ γνωστὸν with τὸ γνωστικόν, τὸ αἰσθητὸν with τὸ αἰσθητικόν, and never realised except in implication therewith.[27]
[27] Plato, Sophistes, pp. 247-248.
The view taken of this matter by Mr. John Stuart Mill, in the third chapter of the first Book of his System of Logic, is very instructive; see especially pp. 65-66 (ed. 4th).
Aristippus (one of the Sokratici viri, contemporary of Plato) and the Kyrenaic sect affirmed the doctrine — ὅτι μόνα τὰ πάθη καταληπτά. Aristokles refutes them by saying that there can be no πάθος without both Object and Subject — ποιοῦν and πάσχον. And he goes on to declare that these three are of necessary co-existence or consubstantiality. Ἀλλὰ μὴν ἀνάγκη γε τρία ταῦτα συνυφίστασθαι — τό τε πάθος αὐτό, καὶ τὸ ποιοῦν, καὶ τὸ πάσχον (ap. Eusebium, Præp. Ev. xiv. 19, 1).
I apprehend that Aristokles by these words does not really refute what Aristippus meant to affirm. Aristippus meant to affirm the Relative, and to decline affirming anything beyond; and in this Aristokles agrees, making the doctrine even more comprehensive by showing that Object as well as Subject are relative also; implicated both with each other and in the πάθος.