[31] Soph. El. v. p. 167, a. 1: οἷον εἰ τὸ μὴ ὄν ἐστι δοξαστόν, ὅτι τὸ μὴ ὂν ἔστιν· οὐ γὰρ ταὐτὸν εἶναι τέ τι καὶ εἶναι ἁπλῶς.
Compare Metaphys. Z. iv. p. 1030, a. 25, and De Interpretatione, p. 21, a. 25-34: ὥσπερ Ὅμηρός ἐστί τι, οἷον ποιητής· ἆρ’ οὖν καὶ ἔστιν, ἠ οὔ; κατὰ συμβεβηκὸς γὰρ κατηγορεῖται τοῦ Ὁμήρου τὸ ἔστιν· ὅτι γὰρ ποιητής ἐστιν, ἀλλ’ οὐ καθ’ αὑτό, κατηγορεῖται κατὰ τοῦ Ὁμήρου τὸ ἔστιν.
It is clear from the above passages that Aristotle was thoroughly aware of the logical fact which Hobbes, James Mill, and Mr. John Stuart Mill, have more fully brought out and illustrated, as the confusion between the two distinct functions of the substantive verb. Many excellent remarks on the subject will be found in the ‘System of Logic,’ by Mr. J. S. Mill (Bk. I. ch. iv. s. 1); also in the ‘Analysis of the Human Mind,’ by James Mill, especially in the recent edition of that work, containing the explanatory notes by Mr. J. S. Mill and Dr. Findlater (Vol. I. ch. iv. p. 174, seq.). Mr. J. S. Mill, however, speaks too unreservedly of this confusion as having escaped the notice of Aristotle, and as having been brought to light only by or since Hobbes. He says (in a note on the ‘Analysis,’ p. 183):— “As in the case of many other luminous thoughts, an approach is found to have been made to it by previous thinkers. Hobbes, though he did not reach it, came very close to it; and it was still more distinctly anticipated by Laromiguière, though without any sufficient perception of its value … in the following words:— ‘Quand on dit, l’être est, &c., le mot est, ou le verbe, n’exprime pas la même chose que le mot être, sujet de la définition. Si j’énonce la proposition suivante: Dieu est existant, je ne voudrais pas dire assurément, Dieu existe existant: cela ne ferait pas un sens: de même, si je dis que Virgile est poète, je ne veux pas donner à entendre que Virgile existe. Le verbe est dans la proposition n’exprime dont pas l’existence réelle; il n’exprime qu’un rapport spécial entre le sujet et l’attribut, &c.’� The passages above cited from Aristotle show that he had not only enunciated the same truth as Laromiguière, but even illustrated it by the same example (Homer instead of Virgil). I shall in another place state more fully the views of Aristotle respecting Existence.
3. The third of these heads of Fallacy — Ignoratio Elenchi — is, when the speaker, professing to contradict the thesis, advances another proposition which contradicts it in appearance only but not in reality, because he does not know what are the true and sufficient conditions of a valid Elenchus. In order to be valid, it must be real, not merely verbal; it must be proved by good syllogistic premisses, without any Petitio Principii; and it must deny the same matter, in the same relations, and at the same time, as that which the thesis affirmed. Thus, it is no contradiction to affirm and deny doubleness of the same body; both affirmation and denial may be true, if you take the comparison against different numbers or different bodies, or at different times. Sometimes persons neglect some of these conditions, and fancy that they have contradicted the thesis, when they have not: this is Ignoratio Elenchi.[32] (If the thesis be an affirmative universal, it is sufficient contradiction if you prove a negative particular against it.)
[32] Soph. El. v. p. 167, a. 21-35: οἱ δὲ παρὰ τὸ μὴ διωρίσθαι τί ἐστι συλλογισμὸς ἢ τί ἔλεγχος, ἀλλὰ παρὰ τὴν ἔλλειψιν γίνονται τοῦ λόγου.
We may remark, by the way, that it is not very consistent in Aristotle to recognize one general head of Sophistical Refutation called Ignoratio Elenchi, after the definition that he has given of the Sophist at the beginning of this treatise. He had told us that the Sophist was a dishonest man, who made it his profession to study and practise these tricks, for the purpose of making himself pass for a clever man, and of getting money. According to this definition, there is no Ignoratio Elenchi in the Sophist, though there may be in the person who supposes himself refuted. The Sophist is assumed to know what he is about, and to be aware that his argument is a fallacious one.
4. The fourth head includes what are called Fallaciæ Consequentis: when a man inverts the relation between predicate and subject in a categorical proposition affirmative and universal, thinking that it may be simply converted or that the subject may be truly affirmed of the predicate; or when, in an hypothetical proposition, he inverts the relation between antecedent and consequent, arguing that, because the consequent is true, the antecedent must for that reason be true also. Honey is of yellow colour; you see a yellow substance, and you infer for that reason that it must be honey. Thieves generally walk out by night; you find a man walking out by night, and you infer that he must be a thief. These are inferences from Signs, opinions founded on facts of sense, such as are usually employed in Rhetoric; often or usually true, but not necessarily or universally true, and therefore fallacious when used as premisses in a syllogism.[33]
[33] Soph. El. v. p. 167, b. 1-18. This head (Fallacia Consequentis) is not essentially distinguishable from the first (Fallacia Accidentis), being nothing more than a peculiar species or variety thereof, as Aristotle himself admits a little farther on — vi. p. 168, a. 26; vii. p. 169, b. 7; viii. p. 170, a. 3. Compare also xxviii. p. 181, a. 25.
5. The fifth head is that of Petitio Principii: a man sometimes assumes for his premiss what is identical with the conclusion to be proved, without being aware of the identity.[34]
[34] Ibid. v. p. 167, a. 38: διὰ τὸ μὴ δύνασθαι συνορᾶν τὸ ταὐτὸν καὶ τὸ ἕτερον.