Aristotle's On Interpretation Ch. 9. segment 18a28-18a33: When one assertion was true, then the other was false - A look at pairs of contradictory assertions about the past
(18a28-18a33) of Ch. 9: When one assertion was true, then the other was false - A look at pairs of contradictory assertions about the past
From Ch. 7 and onwards we concentrate on determining which pairs of contradictory assertions are never true or false together. Such contradictory pairs we seek to set apart from those which are sometimes both true or false. Having established in Ch. 8 that a compound assertion and its contradictory can be false at the same time, we now come to narrow our search to contradictory pairs of simple assertions.
These we studied in Ch. 7 17b27-17b37. There we learned that (a) a simple assertion with a particular as subject is necessarily true when its contradictory proves false and necessarily false when its contradictory proves true. (b) The same we found to be the case with contradictory assertions with a universal as subject when one assertion applies the subject universally and the other non-universally. (c) When contradictories apply their subject non-universally, however, we found that under certain circumstances both assertions prove true.
When the philosopher first distinguished between the three pairs of contradictory assertions, he based these distinctions on a broader discussion about (a) what nouns may occupy the position of subject in an assertion and (b) in what way. Namely, he divided nouns on the basis of whether they signified particulars or universals, and differentiated between those assertions in which the subject applies universally and those where it applies non-universally. This we discussed in Ch 7 17a37-11b1.
Aristotle begins Ch. 9 by revisiting the three contradictory pairs he introduced in Ch. 7. This time, however, he places our focus on the verbs in these assertions.
on the verb as the part of an assertion which situates it in time
Every assertion carries a verb. The verb of each assertion situates it in time. The “runs” in “a cat runs”, for instance, situates the entire assertion in the present. Aristotle considers forms of verbs which situate an assertion in the present as verbs proper (ῥήματα). Verb forms which situate an assertion in past or future time, however, he calls verb inflections (πτώσεις ῥημάτων). Aristotle adresses this topic in more detail in Ch. 3.
In the present chapter, we first distinguish between (i) assertions we formulate with verbs proper and thereby situate in the present, and (ii) assertions we formulate with inflections of verbs and thereby situate in the past, or (iii) the future. We then seek to determine whether contradictory assertions maintain identical relations of truth and falsity in each of these three cases. To put it in different words, what we wish to work out is whether contradictory assertions prove true or false in the same way whether we describe something in the present, past or future.
From the get go, Aristotle instructs us that contradictories situated in the past maintain the same relations of truth and falsity as those in the present. That is, much like “Socrates is wise” is necessarily true when “Socrates is not wise” proves false, so is “Socrates was wise” necessarily true when “Socrates was not wise” proves false and vice versa.
Be that as it may, when it comes to contradictory assertions about the future (e.g. Socrates will be wise - Socrates will not be wise), Aristotle cautions us that to figure out which one happens to be true or false is considerably more complex a task. From that point in the chapter and onward, Aristotle dedicates his instruction in helping us to develop a more sophisticated understanding of what underlies assertions situated in the future.
Key points: (i) Every assertion carries a verb. The verb of each assertion situates the meaning of that assertion in time. (ii) Verbs proper situate assertions in the present. Some inflections of verbs situate assertions in the past while others in the future. (iii) Contradictory assertions that situate their meaning in the past hold the same relations of truth and falsity as those which situate it in the present. (iv) Contradictory assertions which situate their meaning in the future do not.
