AD INCOMMODUM

Bossuet [1] defines the argument ad incommodum[1] as “the argument that brings one into inconvenience” ([1677], p. 131). It is a variant of the refutative use of pragmatic argument by unacceptable or contradictory consequences, S. Absurd.

This pattern  is illustrated with an example designed to refute the doctrines of opponents of absolute political power over bodies and absolute ecclesiastical authority over souls.

If there were no political authority to which one obeys without resistance, men would devour one another; and if there were no ecclesiastical authority to which individuals are obliged to submit their judgment, there would be as many religions as there are heads. Now, it is false [but it is false] that we should allow men to devour one another, or that there should be as many religions as there are heads. Therefore, we must necessarily recognize a political authority to which we obey without resistance, and an ecclesiastical authority to which individuals submit their judgment.
Bishop Jacques-Bénigne Bossuet, Logic for the Dauphin, p. 131. [1990].

The refutation takes the form of two hypothetical syllogisms:

Without absolute political authority, men would devour each other: no AP → D
Without absolute religious authority, religions would multiply: no AR → M

Men must not devour each other: no D
Religions must not multiply: no M

Therefore, we need absolute political authority: AP
Therefore, we need absolute religious authority: AR

The two arguments are presented in strict parallel. This textual or stylistic turn fuses and freezes the two arguments, and therefore the two powers, to the point of their identification [2]. See parallel cases (in French).

[1] Bishop Jacques Bénigne Bossuet, (1627-1704). In Logique du Dauphin / Logic for the Dauphin., 1677. The Dauphin is the heir apparent of the French Kingdom. Quoted after Paris, Éditions universitaires, 1990, p. 131.

[2] This identification excludes, for example, the plurality of religions in an absolute monarchy.