In the previous post, I presented an overview of Robert Alexy’s theory of legal argumentation. I explained that he argues that legal discourse is a type of general practical discourse and that the rationality of discourses is ensured by adherence to argumentative rules.
Alexy formulated six groups of these rules for general practical discourse and another six groups for legal discourse. The subject of this post is the first group of argumentative rules for general practical discourse. They are called basic rules because they ensure a minimum of rationality in argumentation. They are quoted below (Alexy, 1989, p. 188-191):
(1.1) No speaker may contradict him or herself.
(1.2) Every speaker may only assert what he or she actually believes.
(1.3) Every speaker who applies a predicate F to an object a must be prepared to apply F also to every other object which is like to a in all relevant respects.
(1.4) Different speakers may not use the same expression with different meanings.
[…]
(1.3′) Every speaker may assert only those value judgments or judgments of obligation in a given case which he or she is willing to assert in the same terms for every case which resembles the given case in all relevant respects.
Rule (1.1) is logical in nature and without it there can be no meaningful linguistic communication. In turn, rule (1.2) requires sincerity in this communication. Rule (1.3) imposes the obligation that a speaker qualify identical objects in all relevant aspects in the same way. Rule (1.4) requires that speakers agree on the attribution of meanings to the same expression.
Rules (1.1) to (1.4) apply to practical and theoretical discourses, but rule (1.3′) applies only to practical discourse because it obliges the speaker to make the same value judgments and the same judgments of obligation when the situations are equal in all relevant respects. These judgments of obligation refer to actions that are obligatory, permitted, or prohibited.
I emphasize that rule (1.3) does not require that objects be completely identical for the speaker to assign the same predicates, but rather that such objects be identical in all their relevant aspects. This limitation to the equality of relevant aspects also exists in rule (1.3′).
Bibliographic references
ALEXY, Robert. A Theory of Legal Argumentation: The Theory of Rational Discourse as Theory of Legal Justification. Translated by Ruth Adler and Neil MacCormick. 1st ed. New York: Oxford University Press, 1989.
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