ADifferentSolution 407
have so far interpreted it? A heterodox interpretation has been suggested; and
although, in the end, it must be rejected, it is well worth a whirl.
I start from a passage in Galen’s Introduction to Logic. The last Chapter of
the manual opens like this:
Since the Peripatetics write about what are called co-assumptional syllogisms as
though they had some utility whereas I deem them to be superfluous (as I have
shown in my work On Proof ), it is appropriate to say something about them. … One
species of them is like this:
Of what this, that; but that of such-and-such: therefore this of such-and-such.
Or with names:
Of what tree, plant; but tree of plane-tree: therefore plant of plane-tree.
(inst log xix 1–3)⁵⁸
Galen thinks that such co-assumptional arguments are superfluous inasmuch
as they are, as he puts it, ‘epitomes of predicative syllogisms and not a
separate genus of them’ (inst log xix 2).⁵⁹ (Historians of logic usually call the
arguments ‘prosleptic’, transliterating the Greek ‘προσληπτικός’ rather than
translating it.)
It is hard to see why he took them to be epitomes (unless he means no
more than that their characteristic expression is succinct); but a text from
Alexander shows why he took them to be predicative syllogisms:
What Aristotle means is this. In propositions which contain the three terms potentially
within themselves, like the ones he has just set down and, in general, the ones which
Theophrastus calls co-assumptional propositions (for they in a sense contain the three
terms—in ‘Of all of which B, of all of that A too’, the two terms which are already
determined, namely B and A, in a way embrace the third term (the term of which
B is predicated), save that unlike them it is not determined and evident)—in such
propositions, which seem to differ only in expression from predicative propositions, as
Theophrastus showed in his On Affirmation, he says that a proposition taken thus ‘Of
allofwhichB,ofallofthatA’means‘OfwhateverBissaid,ofallofthemAtooissaid’.
(in APr 378.12–23)⁶⁰
Galen’s illustrative sentence
⁵⁸ ἐπεὶ δὲ καὶ περὶ τῶν κατὰ πρόσληψιν ὀνομαζομένων συλλογισμῶν οἱ ἐκ τοῦ Περιπάτου
γεγράφασιν ὡς χρησίμων, ἐμοὶ δὲ περιττοὶ δοκοῦσιν εἶναι καθότι δέδεικταί μοι κἀν τῇ Περὶ
τῆς ἀποδείξεως πραγματείᾳ, προσῆκον εἴη ἄν τι καὶ περὶ τούτων εἰπεῖν. … ἓν μὲν οὖν εἶδός
ἐστι τοῖον· καθ᾿ οὗ τόδε, καὶ τόδε· ἀλλὰ τόδε κατὰ τοῦδε· καὶ τόδε ἄρα κατὰ τοῦδε. καὶ ἐπ᾿
ὀνομάτων· ἐφ᾿ οὗ δένδρον, καὶ φυτόν· δένδρον δὲ ἐπὶ πλατάνου· καὶ φυτὸν ἄρα ἐπὶ πλατάνου.
⁵⁹ οἱ τοιοῦτοι συλλογισμοὶ τῶν κατηγορικῶν ἐπιτομαί τινές εἰσιν, οὐχ ἕτερον γένος αὐτῶν.
⁶⁰ ὃ λέγει τοιοῦτόν ἐστιν, ὅτι ἐν ταῖς τοιαύταις προτάσεσιν, αἳ δυνάμει τοὺς τρεῖς ὅρους ἐν
αὑταῖς ἔχουσιν, ὁποῖαί εἰσιν ἃς ἐξέθετο νῦν καὶ ὅλως αἱ κατὰ πρόσληψιν ὑπὸ Θεοφράστου