What helps are available to give to the dialectician a ready and abundant command of syllogisms? Four distinct helps may be named:[43] (1) He must make a large collection of Propositions; (2) He must study and discriminate the different senses in which the Terms of these propositions are used; (3) He must detect and note Differences; (4) He must investigate Resemblances.
[43] Topic. I. xiii. p. 105, a. 21: τὰ δ’ ὄργανα, δι’ ὧν εὐπορήσομεν τῶν συλλογισμῶν, ἐστὶ τέτταρα, ἕν μὲν τὸ προτάσεις λαβεῖν, δεύτερον δὲ ποσαχῶς ἕκαστον λέγεται δύνασθαι διελεῖν, τρίτον τὰς διαφορὰς εὑρεῖν, τέταρτον δὲ ἡ τοῦ ὁμοίου σκέψις.
The term ὄργανα, properly signifying instruments, appears here by a strained metaphor. It means simply helps or aids, as may be seen by comparing Top. VIII. xiv. p. 163, b. 9. Waitz says truly (Prolegg. ad Analyt. Post. p. 294): “unde fit, ut ὄργανα dicat quæcunque ad aliquam rem faciendam adiumentum afferant.â€�
1. About collecting Propositions, Aristotle has already indicated that those wanted are such as declare Endoxa, and other modes of thought cognate or analogous to the Endoxa:[44] opinions of the many, and opinions of any small sections or individuals carrying authority. All such are to be collected (out of written treatises as well as from personal enquiry); nor are individual philosophers (like Empedokles) to be omitted, since a proposition is likely enough to be conceded when put upon the authority of an illustrious name.[45] If any proposition is currently admitted as true in general or in most cases, it must be tendered with confidence to the respondent as an universal principle; for he will probably grant it, not being at first aware of the exceptions.[46] All propositions must be registered in the most general terms possible, and must then be resolved into their subordinate constituent particulars, as far as the process of subdivision can be carried.[47]
[44] Topic. I. xiv. p. 105, b. 4: ἐκλέγειν μὴ μόνον τὰς οὔσας ἐνδόξους, ἀλλὰ καὶ τὰς ὁμοίας ταύταις.
[45] Ibid. b. 17: θείη γὰρ ἄν τις τὸ ὑπό τινος εἰρημένον ἐνδόξου.
[46] Ibid. b. 10: ὅσα ἐπὶ πάντων ἢ τῶν πλείστων φαίνεται, ληπτέον ὡς ἀρχὴν καὶ δοκοῦσαν θέσιν· τιθέασι γὰρ οἱ μὴ συνορῶντες ἐπὶ τίνος οὐχ οὕτως.
[47] Ibid. b. 31-37: ληπτέον δ’ ὅτι μάλιστα καθόλου πάσας τὰς προτάσεις, καὶ τὴν μίαν πολλὰς ποιητέον — διαιρετέον, ἕως ἂν ἐνδέχηται διαιρεῖν, &c.
2. The propositions having been got together, they must be examined in order to find out Equivocation or double meaning of terms. There are various ways of going about this task. Sometimes the same predicate is applied to two different subjects, but in different senses; thus, courage and justice are both of them good, but in a different way. Sometimes the same predicate is applied to two different classes of subjects, each admitting of being defined; thus, health is good in itself, and exercise is good as being among those things that promote health.[48] Sometimes the equivocal meaning of a term is perceived by considering its contrary; if we find that it has two or more distinct contraries, we know at once that it has different meanings. Sometimes, though there are not two distinct contraries, yet the mere conjunction of the same adjective with two substantives shows us at once that it cannot mean the same in both[49] (λευκὴ φωνή â€” λευκὸν χρῶμα). In one sense, the term may have an assignable contrary, while in another sense it may have no contrary; showing that the two senses are distinct: for example, the pleasure of drinking has for its contrary the pain of thirst; but the pleasure of scientifically contemplating that the diagonal of a square is incommensurable with the side, has no contrary; hence, we see that pleasure is an equivocal term.[50] In one sense, there may be a term intermediate between the two contraries; in another sense, there may be none; or there may be two distinct intermediate terms for the two distinct senses; or there may be several intermediate terms in one of the senses, and only one or none in the other: in each of these ways the equivocation is revealed.[51] We must look also to the contradictory opposite (of a term), which may perhaps have an obvious equivocation of meaning; thus, μὴ βλέπειν means sometimes to be blind, sometimes not to be seeing actually, whence we discover that βλέπειν also has the same equivocation.[52] If a positive term is equivocal, we know that the privative term correlating with it must also be equivocal; thus, τὸ αἰσθάνεσθαι has a double sense, according as we speak with reference to mind or body; and this will be alike true of the correlating privative — τὸ ἀναίσθητον εἶναι.[53] Farther, an equivocal term will have its derivatives equivocal in the same manner; and conversely, if the derivative be equivocal, the radical will be so likewise.[54] The term must also be looked at in reference to the ten Categories: if its meanings fall under more than one Category, we know that it is equivocal.[55] If it comprehends two subjects which are not in the same genus, or in genera not subordinate one to the other, this too will show that it is equivocal.[56] The contrary, also, of the term must be looked at with a view to the same inference.[57]
[48] Topic. I. xv. p. 106, a. 1-8: τὸ δὲ ποσαχῶς, πραγματευτέον μὴ μόνον ὅσα λέγεται καθ’ ἕτερον τρόπον, ἀλλὰ καὶ τοὺς λόγους αὐτων πειρατέον ἀποδιδόναι.