100 a 18I. Ἡ μὲν πρόθεσις τῆς πραγματείας μέθοδον εὑρεῖν, ἀφ᾿ ἧς δυνησόμεθα συλλογίζεσθαι περὶ παντὸς 20τοῦ προτεθέντος προβλήματος ἐξ ἐνδόξων, καὶ αὐτοὶ λόγον ὑπέχοντες μηθὲν ἐροῦμεν ὑπεναντίον. πρῶτον οὖν ῥητέον τί ἐστι συλλογισμὸς καὶ τίνες αὐτοῦ διαφοραί, ὅπως ληφθῇ ὁ διαλεκτικὸς συλλογισμός. τοῦτον γὰρ ζητοῦμεν κατὰ τὴν προκειμένην πραγματείαν.
25Ἔστι δὴ συλλογισμὸς λόγος ἐν ᾧ τεθέντων τινῶν ἕτερόν τι τῶν κειμένων ἐξ ἀνάγκης συμβαίνει διὰ τῶν κειμένων. ἀπόδειξις μὲν οὖν ἐστίν, ὅταν ἐξ ἀληθῶν καὶ πρώτων ὁ συλλογισμὸς ᾖ, ἢ ἐκ τοιούτων ἃ διά τινων πρώτων καὶ ἀληθῶν τῆς περὶ αὐτὰ 30γνώσεως τὴν ἀρχὴν εἴληφεν· διαλεκτικὸς δὲ συλλογισμὸς 100 b 18ὁ ἐξ ἐνδόξων συλλογιζόμενος. ἔστι δὲ ἀληθῆ μὲν καὶ πρῶτα τὰ μὴ δι᾿ ἑτέρων ἀλλὰ δι᾿ αὑτῶν ἔχοντα τὴν πίστιν· οὐ δεῖ γὰρ ἐν ταῖς 20ἐπιστημονικαῖς ἀρχαῖς ἐπιζητεῖσθαι τὸ διὰ τί, ἀλλ᾿ ἑκάστην τῶν ἀρχῶν αὐτὴν καθ᾿ ἑαυτὴν εἶναι πιστήν. ἔνδοξα δὲ τὰ δοκοῦντα πᾶσιν ἢ τοῖς πλείστοις
I. The purpose of the present treatise is to discover Introduction (I. 1–3). The design of the treatise. a method by which we shall be able to reason from generally accepted opinions about any problem set before us and shall ourselves, when sustaining an argument, avoid saying anything self-contradictory. First, then, we must say what reasoning is and what different kinds of it there are, in order that dialectical reasoning may be apprehended; for it is the search for this that we are undertaking in the treatise which lies before us.
Reasoning is a discussion in which, certain things The different kinds of reasoning: having been laid down, something other than these things necessarily results through them. Reasoning is demonstration when it proceeds from premises which (a) Demonstrative. are true and primary or of such a kind that we have derived our original knowledge of them through premises which are primary and true. Reasoning is (b) Dialectical. dialectical which reasons from generally accepted opinions. Things are true and primary which command belief through themselves and not through anything else; for regarding the first principles of science it is unnecessary to ask any further question as to ‘why,’ but each principle should of itself command belief. Generally accepted opinions, on the other hand, are those which commend themselves