• Lat. iudicium, “judgment”. legal action; judgment; capacity to judge
Locke  opposes the ad judicium argument, declared valid, to three kinds of argument he considers fallacious, the arguments ad ignorantiam, ad hominem and ad verecundiam (Lat. verecundia, modesty); S. Collections (2).
The argument ad judicium is defined as:
The using of proofs drawn from any of the foundations of knowledge or probability. This I call argumentum ad judicium. This alone of all the four, brings true instruction with it, and advances us in our way to knowledge. (Locke , Vol. 2, p. 411)
The following declaration shows that this validity is derived not only from judgment but also from “the things themselves”:
[truth] must come from proofs and arguments, and light arising from the nature of things themselves. (Id., p. 411-412).
So, the ad judicium argument, is based on scientific procedures and criteria (“foundations of knowledge or probability”), and develops object-based knowledge. In any case, this mode of reasoning excludes the passions and distrusts the speech, S. Ornament and argument.
Ad judicium is not strictly speaking an argument scheme in itself, but instead covers the whole scientific methodology. From Locke’s definitions, it follows that the correct argumentative method is the name of scientific method when applied to social questions and human projects.
Ad hominem and ad verecundiam arguments also appeal to judgment, at least to a calculus: ad hominem appeals to consistency; ad verecundiam is based on a sense of modesty or personal insufficiency that can be well grounded or not. They are nonetheless considered fallacious because they are subjective. Subjective does not here mean “arbitrary”, but rather nonuniversal, context-bound, taking the circumstances of the speech situation and the speaker’s transitional state of knowledge into account, what he or she knows, believes or dares say or not.
Argument thus conceived rejects the speaker and his system of knowledge as consistently relative. It is the antithesis of what Grize calls « a logic of subjects », S. Schematization
Ad judicium, a homonymic label
Various non-equivalent, definitions are attached to the ad judicium label. This can prove somewhat confusing.
(1) Perhaps referring to Locke, Whately considers that the ad judicium label designates “most likely the same” as the ad rem argument (, p. 170), that is, argument to the matter, or to the thing itself.This identification is grounded in the fact that Locke considers that true knowledge derives “from the nature of things themselves” (see supra).
In this case the terminology would just be redundant, which is relatively benign.
(2) A dictionary of theology defines ad judicium as: “an argumentation calling on common sense and general opinion to validate a position” which is something quite different, and totally opposed to Locke’s perspective, if we consider his positions on rhetoric, S. Ornamental fallacy.
(3) And Bentham uses the ad judicium label to designate a series of fallacies of confusion (Bentham ), S. Political Arguments: Two collections.
The terminological and conceptual field covered by the ad judicium label can thus be arranged as follows:
— In Locke’s sense scientific reasoning, based on things.
— In Whately’s sense, same as ad rem, argument on the merits of the case.
— In theology, argument based on the consensus of nations.
— In Bentham’s sense, the ad judicium fallacies are manoeuvres tending to obstruct the sound exercise of judgement.