CONSISTENCY
The basic expression of argumentative coherence or consistency is non-contradiction, see non-contradiction; absurd; ad hominem.
The consistency requirement is particularly important in systems of regulation of human behavior, religion, law, and ordinary institutional or family rules.
The consistency requirement is expressed a contrario in the refutation strategy mentioned in Aristotle’s Rhetoric, topic # 22:
Another line of argument is to refute your opponent’s case by noting any contrast or contradiction of dates, acts or words that it anywhere displays. (1400a15; RR p. 373).
1. After the event as before
Topos ≠5, “On the consideration of time” appeals to consistency. This theme is not explicitly stated, but is presented by two examples:
If before doing the deed I had bargained that, if I did it, I should have a statue, you would have given me one. Will you not give me one now that I have done the deed? (Rhet, II, 23, 5; RR, p. 361).
The situation is this:
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- X (asks nothing and) performs a deed (perhaps an impulsive heroic act)
- Afterwards, he asks for a reward.
- Argument: if he had asked before, a reward would have been agreed upon
The hero feels that all feats must be paid for as such. It is as if the definition of the word feat includes the characteristic “deserves a reward”:
L1: — If you do it, you’ll get…
L2: — I have done it, and done well, so give me …
This argument scheme express the disappointment of someone who reports finding a wallet and does not receive a reward.
2. Human (in)consistency
Consistency may be the rule, but inconsistency is a fact of life. This is what the argument scheme #18 says:
Men do not always make the same choice on a later and on an earlier occasion, but reverse their previous choice. (Rhet, II, 23, 18; RR, p. 371)
This argument scheme is materialized in the following enthymeme:
When we were exiles, we fought in order to return; now that we have returned, it would be strange to choose exile in order not to have to fight. (ibid.)
The enthymeme seems to assume the following situation. In the past, the exiles fought to return home, and they returned. In the present situation, they are suspected of refusing to fight, and preferring exile. They deny the charge with this enthymeme, which is a claim of consistency, as in:
You fought for this position, now you can’t accept being thrown out like this!
This is a kind of positive ad hominem argument; it may presuppose an a fortiori: “We fought to return to our homeland, a fortiori we will fight not to be thrown out of it!”
The accusers reply “Men do not always make the same choice, etc.”
The opposing party argues from a contrary view of human nature; the two opinions “men are constant / inconstant”, are equally probable (see ibid I, 2, 14; p. 25). They can thus be the basis for two antagonistic conclusions.
S. Ad hominem; A fortiori.
3. Consistency of the legal system and stability of the objects of the law
Lat. arg. a cohærentia, de cohærentia, “to form a compact whole”.
3.1 Principle of coherence of laws, a cohærentia
This principle requires that, within a legal system, one norm cannot conflict with another; the system does not allow antinomies. An argument can therefore be rejected if it leads to the view that two laws are contradictory; this is a form of argument from the absurd.
In practice, this principle excludes the possibility of the same case being decided in two different ways by the courts.
According to this principle, if two laws contradict each other, they are only seemingly contradictory, and, consequently, they must be interpreted in such a way as to eliminate the contradiction. If one of these laws is obscure, it must be clarified by reference to a less doubtful one.
The argument a cohærentia is used to resolve conflicts of norms. To prevent such conflicts, the legal system provides for adages, which are meta-principles of interpretation, such as “the most recent law takes precedence over the oldest”. These adages are interpretive meta-principles, coming from Roman law and sometimes expressed in Latin: “lex posterior derogat legi priori”.
3.2 Principle of the stability of the object of the law, in pari materia
Lat. in pari materia: lat. par, “equal, like”; materia, “topic, subject” argument “in a similar case, on the same subject”.
The argument a cohærentia deals with the formal non-contradiction of laws in a legal system. The argument in pari materia, or argument “on the same subject”, expresses a substantive form of consistency. It requires that a law be understood in the context of other laws that have the same goal or refer to the same beings, that is to say the same beings (persons, things, actions) or the same subject.
The given definition of the subject of the law must be stable and consistent. The application of the argumentation a pari presupposes the stability of the legal categories. see Classification; A pari.
This principle of consistency leads the legislator to harmonize the system of laws on the same subject. What constitutes the same subject and the set of laws on the same subject may be questioned. For example, anti-terrorist laws, are a package of different legal provisions, for which it is necessary to ensure that the definition of “terrorism” remains the same in each of the passages that use the term. If this is not the case, these laws need to be made consistent, which means that they themselves need to be underpinned by a consistent policy.
The two topoi discussed in the two following paragraphs are taken from Aristotle’s Rhetoric. They are based on the two incompatible, but equally recognized substantive topoi, “human conduct is, or ought to be consistent” and “human conduct is inconsistent”.
4. Argument from narrative inconsistency
As a special case of ad hominem argumentation, showing inconsistencies in the accusatory narrative can refute an accusation:
S1: — You are the heir, you benefit from the crime, you killed to inherit!
S2: —Then, I should have killed the other legatee too.
The prosecution will have to prove that S2 also intended to murder the other heir, or otherwise find an alternative motive. The defense starts from the hypothesis proposed by the prosecution to show that the actions of the suspect do not fit into the proposed scenario; the accusatory narrative contains flaws or contradictions.
The incoherent accusation argument exploits a basic principle of practical rationality: the suspect’s actions must be consistent with his or her claimed goal. The defendant can refute the accusatory narrative by showing that, according to hat narrative, he acted inconsistently:
You say I’m the killer. But it has been proven that just before the crime, I spent an hour in the cafe in front of the victim’s house, everyone saw me. It is not consistent behavior for a murderer to show himself at the scene of the crime.
Any weakness found in the prosecution’s scenario can then be used to exonerate the defendant.
The principle of consistency of laws and the principle of stability of the subject of the law concern the coherence of the legal system. The argument from the inconsistency of the narrative exploits the resources of narrative rationality: all the narratives offered as excuses, all the narratives mixed with argumentation are vulnerable to this kind of refutation.
Conversely, the argument seems plausible and reasonable because the story is so, and because the speaker knows how to tell it.
The strategies described in the topoi # 22, 25 and 27 and probably 18 (see above) of the Rhetoric are relevant to this discussion (Aristotle, Rhet., II, 23), see Collections 2.