Sextus Empiricus Pyrrhoniae Hypotyposes 1.14.69

[69] And according to Chrysippus, who shows special interest in irrational animals, the dog even shares in the far-famed ‟Dialectic.” ¹ This person, at any rate, declares that the dog makes use of the fifth complex indemonstrable syllogism ² when, on arriving at a spot where three ways meet, after smelling at the two roads by which the quarry did not pass, he rushes off at once by the third without stopping to smell. For, says the old writer, the dog implicitly reasons thus: ‟The creature went either by this road, or by that, or by the other: but it did not go by this road or by that: therefore it went by the other.”