Aristotle, Prior Analytics, Book I, Chapter 1

by William C. Michael

In this lesson, we study the first chapter of Aristotle’s Prior Analytics, the third book of the Organon. For tutorial resources on this lesson, please see the Academy YouTube channel. This lesson is studied in the Academy’s Classical Reasoning II course. The text below is adapted from Thomas Taylor’s translation of Aristotle’s Prior Analytics

Aristotle (384–322 BC)

In the first place it is requisite to say what the subject is of the present treatise, and for the sake of what it is undertaken; namely, that it is concerning demonstration, and for the sake of demonstrative science. Afterwards, it is requisite to define what a proposition is, what a term, and what a syllogism; and also what kind of a syllogism is perfect, and what kind is imperfect. In the next place it must be shown what it is for a thing “to be in” or “not to be in” a certain whole, and what we say it is to be predicated of “all” or “none” of a certain multitude.


A proposition, therefore, is a sentence affirming or denying something (a predicate) of something (a subject). And this is universal, or particular, or indefinite. But I denominate “universal” the being present with all or with none; “particular”, the being present with some or not with some, or not with all; and the “indefinite”, the being present or not being present without the universal or particular; such, for instance, as that there is the same science of contraries, or that pleasure is not good.

But a demonstrative proposition differs from a dialectical proposition in this; that a demonstrative proposition is an assumption of one part of contradiction (i.e., the truth), but the dialectical proposition is an interrogation of contradiction (i.e., the true and the false).

So far, however, as pertains to the framing of a syllogism from either proposition, the one in no respect differs from the others. For he who demonstrates, and he who interrogates both syllogize, assuming that something is present with or not present with something. Hence a syllogistic proposition, indeed, will simply be an affirmation or negation of something (a predicate) concerning something (a subject), after the manner mentioned above.

But a proposition is demonstrative if it is true, and is assumed through hypotheses from the beginning. And a dialectical proposition, with respect to him who enquires, is an interrogation of a contradiction; but with respect to him who syllogizes, is an assumption of that which is seen and probable, as we have observed in the Topics.

What, therefore, a proposition is, and in what the syllogistic, demonstrative, and dialectical proposition differ from each other, will be accurately shown in the following treatises; but for the present purpose, what has now been determined by us may suffice.


But I call that a term into which a proposition is dissolved; as, for instance, that which is predicated (the predicate), and that of which it is predicated (the subject), whether “to be” or “not to be” is added or separated.


And a syllogism is a discourse in which, certain things being admitted (i.e., premises), something else, different from the things admitted (i.e., a conclusion), necessarily happens, in consequence of the existence of these admitted propositions. I say, that in consequence of these admitted propositions, something else happens. And when I say that something else happens through these, I mean that there is no need of any external term, in order to the existence of the necessary consequence. Hence I call that a perfect syllogism, which requires nothing else besides the things assumed in order that the necessary consequence may be apparent. But I denominate that an imperfect syllogism which requires one or more things, which through the supposed terms are necessary, and yet are not assumed through propositions. And it is the same thing, for one thing to be in all of another, and for one thing to be predicated of all of another, when no part or member can be assumed of the subject, of which the other may not be asserted: and to be predicated of none is assumed after a similar manner.

In this first chapter of Prior Analytics, Aristotle identifies the subject of the book, which is to teach the science of demonstration. He also defines the most principal terms in the subject: proposition, term, and syllogism.




Mr. William C. Michael is the founding headmaster of the <a href=”">Classical Liberal Arts Academy</a>. He graduated from Rutge

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William C. Michael

William C. Michael

Mr. William C. Michael is the founding headmaster of the <a href=”">Classical Liberal Arts Academy</a>. He graduated from Rutge

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