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Aristotle, On Interpretation. Chapter 09

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In this lesson, we will study chapter 09 of Aristotle’s work “On Interpretation”. translated by Thomas Taylor. To complete the objectives of this lesson, complete the following tasks:

  1. Study the Prelection.
  2. Read through the lesson once for familiarity.
  3. Study the lesson for mastery.
  4. Complete the lesson assessment.


by William C. Michael

Thus far, Aristotle has provide us with an introduction to enunciative speech. St. Thomas Aquinas summarizes these teachings in a way that is very helpful for us, which I’d like to share in this prelection.

First, Aristotle has taught that there are five divisions of enunciations. These divisions are made with reference to:

  1. Unity: Simple and Compound enunciations
  2. Quality: Affirmative and Negative enunciations
  3. Quantity: Universal (Every), Particular (Some), Indefinite, Singular enunciations
  4. Time: Present, Past, Future enunciations
  5. Matter: Necessary, Impossible, Contingent enunciations

Second, we learned that every affirmation has a corresponding negation (contradiction) and that, in all times, these cannot both be true (or false) at the same time–except for indefinite enunciations.

Third, while the above is true of most enunciations, when we speak of contingent, future, singulars this is found not to be true. This is the subject of the present lesson.

Before beginning, it is important to understand that “contingent” things are things that are neither necessary nor impossible. There are three kinds of contingent things. They are things that happen by:

  1. Chance: infrequent events that happen by chance or fortune
  2. Choice: things that have no natural inclination, but are determined by choice:
  3. Nature: things that normally happen, but do not necessarily do so.

With these things understood, let us begin chapter 9.


Aristotle, translated by Thomas Taylor and William C. Michael

1. In those things (i.e., enunciations), therefore, which are (i.e. present tense), and in those which have come to be (i.e., past tense), it is necessary that affirmation or negation should be true or false; and in universals, indeed, as universals, that always the one should be true, but the other false; and also in particulars, as we have shown. But in universals not universally pronounced this is not necessary; concerning which also we have spoken.

This, however, is not similarly the case in things singular and future.1

1 This note introduces the subject of chapter 9: “Whether in singular enunciations about the future in contingent matter it is necessary that one of the opposites be determinately true and the other determinately false?” (Aquinas). Now, it is acceptable for us to accept this by faith, trusting in St. Thomas Aquinas’ approval, but Aristotle proves it below.

2. For if every affirmation or negation is true or false, it is also necessary that every thing should exist, or should not exist.2 For if one person says that something will be, but another says it will not be; it is evident that one of them necessarily speaks truly, if every affirmation or negation is true or false; since both will not subsist at one and the same time in things of this kind. Thus, if it is true to say “This thing is white.”, or “This thing is not white.”, it is necessary that it should be white, or not white. And if it is white, or not white, it was true to affirm or deny that it is white, or not white. Also if it is not, it is falsely said to be so; and if it is falsely said to be so, it is not.

2 “Truth” is defined as the enunciation of that which exists in reality, therefore, for an enunciation concerning singular future events to be “true” whatever is asserted must necessarily take place in the future. If this is so, then things which happen would happen by necessity and nothing would be contingent. Aristotle uses this absurd conclusion to prove that what is true of other enunciations is not true of future singular enunciations.

3. Hence it is necessary, that either affirmation or negation should be true or false. Nothing, therefore, either is, or is generated either fortuitously, or casually3, nor will it be or not be, but all things are from necessity, and not casually, or in any manner whatever. For either he who affirms speaks truly, or he who denies; since otherwise, it might similarly be generated or not generated. For that which subsists casually, does not more subsist, or will not more subsist in this way than in that.

3 “Fortuitously” = by fortune; “casually” = by chance. These refer to contingent events.

4. Again, if a thing is now white, it was true to say before, that it will be white so that it was always true to say, of any thing which is generation or becoming to be, that it is, or will be; and it is not possible that this is not or will not be. But with respect to that which it is impossible should not pass into existence, it is impossible that it should not be generated. And with respect to that which cannot not be generated, it is necessary that it should be generated. And hence nothing will be casual, nor subsist fortuitously; for if fortuitously, it will not be from necessity.

5. Nor can it be said that neither of them is true3; as, for instance, that it neither will be, nor will not be. For in the first place, the affirmation being false, the negation will not be true.

3 Here Aristotle makes a second argument that opposing future singular enunciations cannot both be false.

6. And, besides, if it was true to say, that a thing is white and at the same time great, it is necessary that both should exist. But if it was true to say it will be tomorrow, it is necessary that it should be tomorrow. And if it was true to say it neither will be, nor will not be tomorrow, it will not be that which may happen casually, or in any way; as, for instance, a naval engagement. For it would be requisite that a naval engagement should neither take place, nor should not take place.

7. These, therefore, and other such like absurdities4 will happen if of every affirmation and negation, either in things universal considered as universal, or in particulars, it is necessary that the one of opposites should be true, and the other false; viz. that nothing in things generated will be casual, but that all things will be, and will be generated from necessity. Hence it will neither be requisite to consult, nor to be busily employed; so as that if we do this particular thing, some thing definite will take place; but if not, it will not take place.

4 “The Philosopher has shown—by leading the opposite position to what is unlikely—that in singular future enunciations truth or falsity is not determinately in one of the opposites, as it is in other enunciations. Now he is going to show that the unlikely things to which it has led are impossibilities.” (Aquinas)

8. For nothing hinders, but that one person may for ten thousand years assert that this will take place, and that another person may assert that it will not; so that from necessity it will come to pass, that it was then true to assert either of them.

9. Nor is it of any consequence whether some person should utter a contradiction, or should not. For it is evident that the things thus subsist, although the one should not affirm any thing, but the other should deny it. For not because a thing is affirmed or denied, will it, therefore, be or not be; nor will it more be or not be for ten thousand years, than for any time whatever. Hence if a thing will thus subsist in every time, that it will be true to assert the one of these, it was necessary that this should take place; and every thing generated will always so subsist, as that it will be generated from necessity. For when any one truly says that it will be, it is not possible that it should not be generated; and with respect to that which is generated, it was always true to say, that it will be.

10. But these things are impossible. For we see that there is a beginning of things which will be, from our deliberating and acting; and, in short, we see in things which do not always energize, that there is a power of similarly being and not being, in which both may happen, viz. to be and not to be; so that also they may be generated, and may not be generated. And many things are manifest to us which thus subsist. Thus, for instance, it is possible that this garment may be cut in pieces, and it may not be cut in pieces, but prior to this may be worn out. In like manner also, it is possible that it may not be cut in pieces; for it would not prior to this have been worn out, unless it had been possible that it might not be cut in pieces. The same thing, therefore, must also be said in other generations, which are spoken of according to a power of this kind.

11. Hence it is evident, that all things neither are, nor are generated, or becoming to be, from necessity; but that some things have a casual subsistence, and that affirmation respecting them is not more true than negation; and that there are other things in which one of these subsists more frequently, and for the most part5, and yet it may happen that the one of these may take place, but the other not.

5 “more frequently and for the most part” – that is, contingent things that are contingent by nature, which normally occur, but not necessarily. See prelection for the three kinds of contingent events.

12. It is necessary, therefore, that being should be when it is, and that non-being should not be, when it is not. It is not, however, necessary either that every being should be, or that non-being should not be. For it is not the same thing for every being to be from necessity when it is, and to be from necessity simply. And the like must be asserted of non-being.

13. There is also the same reasoning in contradiction. For it is necessary that every thing should either be or not be, and also that it will be, or will not be. Yet it is not necessary to speak of one of them separately. I say, for instance, it is necessary, indeed, that there will be or will not be a naval engagement tomorrow, yet it is not necessary that there should be a naval engagement, nor that there should not be6. It is necessary, however, that it should either be or not be.

6 That one or the other opposite will be true is necessary, but it is not true that either of them is necessary.


14. Hence, since assertions and things are similarly true, it is evident that in things which so subsist, that in whatever manner they may happen to be, contraries may also happen, it is necessary that contradiction should likewise subsist in a similar manner; which happens to be the case, in things which are not always, or which not always are not7. For of these it is necessary that one part of the contradiction should be true or false; not, however, this thing or that, but just as it may happen. It is also necessary that the other part should be more true; yet it is not necessary that it should now be true or false. Hence it evidently is not necessary that of every affirmation and negation of opposites, the one should be true, but the other false. For the like does not take place in things which are not indeed, but which either may be, or may not be, as in things which are; but it happens as we have said.

7 Things which are “always” are necessary things. Things which ae “always not” are impossible things. Things which “are not always…or…not always are not” are contingent things.

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