A Stoic proof turned against Celsus
He sets down, by way of hypothesis, certain things that are impossible for God and unfitting for him, and says: “If these things were prophesied of the God over all, must we, because they are foretold, believe such things of God?” He thinks he is establishing that, even if the prophets had truly foretold such things of the Son of God, it was impossible that one should have to believe the predictions that he suffered or did them. To this we must say that his hypothesis, being absurd, would produce conditionals that end in statements that contradict each other. This is shown as follows.
If the true prophets of the God over all should say that God would be a slave, or always be sick, or die, these things will happen to God, for the prophets of the great God must speak without falsehood. But also, if the true prophets of the God over all say these same things, then, since what is impossible by nature is not true, what the prophets say would not happen to God. Now when two conditionals end in statements that contradict each other, by the theorem called the argument from two conditionals, the antecedent common to both conditionals is refuted. Here that antecedent is that the prophets foretell that the great God will be a slave, or fall sick, or die. The conclusion is therefore: the prophets did not, then, foretell that the great God would be a slave, or fall sick, or die. And the argument falls under a mode of this kind: if the first, then the second; if the first, then not the second; therefore not the first.
The Stoics also apply this mode to a concrete case, saying: if you know that you are dead, you are dead; if you know that you are dead, you are not dead; and it follows: therefore you do not know that you are dead. They establish the conditionals in this way. If you know that you are dead, what you know is so; therefore it is so that you are dead. And again: if you know that you are not dead, and what you know is so, you are not dead; and since a dead man knows nothing, it is plain that if you know that you are dead, you are not dead. And from both conditionals there follows, as I said before: therefore you do not know that you are dead. Something like this holds also for Celsus’s hypothesis, in the words of his that we set out above.
Greek
Ἐπεὶ δ᾿ ἀδύνατά τινα καὶ ἀπρεπῆ θεῷ καθ᾿ ὑπόθεσιν τιθείς φησιν· εἰ ταῦτα προφητεύοιτο περὶ τοῦ ἐπὶ πᾶσι θεοῦ, ἆρ᾿, ἐπεὶ προλέγεται, πιστεύεσθαι δεῖ τὰ τοιαῦτα περὶ θεοῦ; καὶ νομίζει κατασκευάζεσθαι ὅτι, κἂν ἀληθῶς ὦσι προειρηκότες οἱ προφῆται περὶ υἱοῦ θεοῦ τοιαῦτα, ἀδύνατον ἦν αὐτὸν παθεῖν ἢ δρᾶσαι χρῆναι πιστεύειν τοῖς προειρημένοις· λεκτέον ὅτι ἡ ὑπόθεσις αὐτοῦ ἄτοπος οὖσα ποιήσαι ἂν συνημμένα εἰς τὰ ἀλλήλοις ἀντικείμενα λήγοντα, ὅπερ οὕτω δείκνυται. εἰ οἱ ἀληθῶς προφῆται τοῦ ἐπὶ πᾶσι θεοῦ δουλεύειν ἢ νοσεῖν ἀεὶ ἢ τεθνήξεσθαι φήσαιεν τὸν θεὸν, συμβήσεται ταῦτα περὶ τὸν θεὸν, ἀψευδεῖν γὰρ ἀνάγκη τοὺς τοῦ μεγάλου θεοῦ προφήτας· ἀλλὰ καὶ εἰ οἱ ἀληθῶς προφῆται τοῦ ἐπὶ πᾶσι θεοῦ τὰ αὐτὰ ταῦτά φασιν, ἐπεὶ τὰ τῇ φύσει ἀδύνατα οὐκ ἔστιν ἀληθῆ, οὐκ ἂν συμβαίη περὶ τὸν θεὸν ἃ λέγουσιν οἱ προφῆται. ὅταν δὲ δύο συνημμένα λήγῃ εἰς τὰ ἀλλήλοις ἀντικείμενα τῷ καλουμένῳ „διὰ δύο τροπικῶν“ θεωρήματι, ἀναιρεῖται τὸ ἐν ἀμφοτέροις τοῖς συνημμένοις ἡγούμενον, ὅπερ ἐν τούτοις ἐστὶ τὸ προλέγειν τοὺς προφήτας τὸν μέγαν θεὸν δουλεύειν ἢ νοσήσειν ἢ τεθνήξεσθαι. συνάγεται οὖν τὸ οὐκ ἄρα προεῖπον οἱ προφῆται τὸν μέγαν θεὸν δουλεύσειν ἢ νοσήσειν ἢ τεθνήξεσθαι, καὶ ὑπάγεταί γε ὁ λόγος τρόπῳ τοιούτῳ· εἰ τὸ πρῶτον, καὶ τὸ δεύτερον· εἰ [οὐ] τὸ πρῶ τον, οὐ τὸ δεύτερον· οὐκ ἄρα τὸ πρῶτον. φέρουσι δὲ καὶ ἐπὶ ὕλης τὸν τρόπον τοῦτον οἱ ἀπὸ τῆς Στοᾶς, λέγοντες τό· εἰ ἐπίστασαι ὅτι τέθνηκας, τέθνηκας· εἰ ἐπίστασαι ὅτι τέθνηκας. οὐ τέθνηκας· ἀκολουθεῖ τὸ οὐκ ἄρα ἐπίστασαι ὅτι τέθνηκας. τὸν τρόπον δὲ τοῦτον κατασκευάζουσι τὰ συνημμένα· εἰ ἐπίστασαι ὅτι τέθνηκας, ἔστιν ὃ ἐπίστασαι, ἔστιν ἄρα τὸ τέθνηκας. καὶ πάλιν· εἰ ἐπίστασαι ὅτι οὐ τέθνηκας, καὶ ἔστιν ὃ ἐπίστασαι, οὐ τέθνηκας, ἐπεὶ δὲ ὁ τεθνηκὼς (οὐδὲν) ἐπίσταται, δῆλον ὅτι, εἰ ἐπίστασαι ὅτι τέθνηκας, οὐ τέθνηκας. καὶ ἀκολουθεῖ, ὡς προεῖπον, ἀμφοτέροις τοῖς συνημμένοις τὸ οὐκ ἄρα ἐπίστασαι ὅτι τέθνηκας. τοιοῦτόν τι ἐστὶ καὶ περὶ τὴν Κέλσου ὑπόθεσιν, λέγοντος ἣν προεξεθέμεθα λέξιν.