one or the other, for he cannot drown unless he is at sea. Either he does not drown in it—in which case he has not gone to sea—or he has gone to sea. Going to sea and drowning may occur together.

Examples abound, such as our saying: “This is alive, or it lacks knowledge, power, hearing, sight, or speech.” If life is present, one of the two alternatives holds; if life is absent, these attributes are absent. Yet something may be alive without possessing these attributes. The same applies when one says: “This person is ritually purified, or he is not praying.” If prayer is absent, ritual purity is absent; if ritual purity is present, the other alternative holds. Thus, one or the other must hold.

The same applies to every instance involving the absence of a condition and the presence of that which depends upon it. When the alternatives are the presence of that which depends upon a condition and the absence of the condition, the proposition precludes joint falsity. For the condition must either be present or absent; when it is absent, the condition is absent. Thus, either that which depends upon the condition must be present, or the condition must be absent.

They then divide conjunctive syllogisms into the four figures. The middle term may be the predicate in the major premise and the subject in the minor premise—this is the natural figure, which yields all four types of conclusion: particular and universal, affirmative and negative. Alternatively, the middle term may be the predicate in both premises: this is the second figure, which yields only negative conclusions. Or it may be the subject in both, yielding only particular conclusions. The fourth figure yields particular conclusions and universal negative conclusions, but it is far removed from natural reasoning.

Then, when they wish to demonstrate how the second and third figures yield conclusions, or to establish other conclusions, they need to reason by means of contradictories, converses, and contrapositives. For the truth of