and which he designates a logical fallacy, it is assumed that man is mortal rather than immortal or both together, but also that animals can be mortal or immortal, that man is an animal, etc. That Aristotle himself realized (An. Po. 96b7). But whereas in a syllogism nothing prevents us from assuming just those propositions, in a division there is no syllogism to justify the premisses-just because it is not a correct syllogism, perhaps not a syllogism at all. So there is no reason why animals should be subdivided into mortal or immortal, rather than into living and dead, or into young and old. That is to say: since no conclusion can be derived from such premisses, these are justified only by the fact that we already know where the division is leading. Plato always recommends the greatest attention in dividingwhich Aristotle did after him-in order to avoid the mistake of assuming, as differentia of species, properties which might be too weak in comparison with the genus (family); he also exhorts us not to pursue the division only with a view to a pre-established aim-in order to avoid the risk of disregarding the natural sub-divisions of species, and of coming to the wanted species too early, missing some middle division. In spite of this, both the particular divisions and the object of the investigation are wellknown to the one who employs such divisions: in the Sophist and in the Statesman, in fact, it is the Stranger who performs the division of such complex genera, that is one who, as opposed to Socrates, is a wise man. Divisions are established specifically with a view to particular investigations. Even if that does not mean that Plato goes against his own rule, it is certain that, on occasion, a genus that has been previously divided into two or more species, may be divided into further different ones, in order to reach to a different goal (cf. Rep. 470b-c and Polit. 262d-e). After all, skill at operating divisions is not logical-deductive, nor is it a question of following any strict ('mechanical') method: on the contrary, it is a question of choosing things that everybody knows, and arranging them in a chain which leads from a more comprehensive genus to a peculiar and 'atomic' species. That comes out clearly from the first division in the Sophist: the Stranger says that the practice of divisions must begin from an easy case,