Some argument schemes are designated by Latin labels, S. A/ab —; Ad —; Ex —. This entry lists the labels using the Latin preposition ad. In classical Latin, the preposition ad is constructed with the accusative and introduces a goal complement; the phrase “argument ad hominem” reads “argument addressing the person”.
According to Hamblin, the oldest scheme in this grouping is ad hominem, which appears in the Latin translations of Aristotle; this naming method was popularized by Locke ([1690]) and by Bentham ([1824]), and most of these terms seem to be nineteenth or twentieth century creations (Hamblin 1970, p. 41; p. 161-162).

1. A list of “ad + N” arguments

2. Characteristics of the “ad + N” family

2.1 A productive pattern

There are many more “ad +N” arguments than there are “a / ab + N” arguments. Only the “ad +N” construction is still productive; the pattern is popular and mocked (ad bananum argument).

2.2 Origin of the labels

Some of these names have been defined and used by Locke and Bentham, S. Collections (III).

Locke has defined the arguments:

ad hominem                      ad judicium
ad ignorantiam                   ad verecundiam

Bentham has defined the arguments:

2.3 Semantic subsets of “ad + N” arguments

These arguments refer to very different strategies. Nonetheless, some groupings can be proposed according to their semantic content.

(i) Arguments bound to affects, emotions, often via positive interest (rewards) or negative results (threats):

(ii) Arguments involving a subjective system of beliefs, not universal, questionable:

Categories (i) and (ii) list arguments often considered as misleading, insofar as they express the subjectivity of the speaker. In other words, they are related to the ethotic and pathemic components

(iii) Arguments dealing with the substance of the issue (contrasting with the subjective series (i) and (ii))

ad iudicium                      ad rem

1. The fallacy of accident

The fallacy of accident is the first on Aristotle’s list of fallacies independent of discourse, S. Fallacies (II): Aristotle’s foundational list.
The idea is that a valid syllogistic inference develops in the same category domain, for example, the class of animals:

Socrates is a man, man is a mammal, so Socrates is a mammal,

whereas the following fallacious inference develops from an accident:

Socrates is white, white is a color, so Socrates is a color.

The word accident is taken in its philosophical meaning, which contrasts accident with essence. A being is characterized by a set of essential features that determine its place in a scientific classification: its generic features express its genus and its specific difference indicates its species. Unlike “— is a mammal”, which is constantly true of all dogs, the truth of the accidental predicate “— is tired” is circumstantial, it may be true of a dog at a given time but become false as soon as the dog’s condition changes.

The fallacy of accident occurs when an accidental characteristic of a being is mistaken for an essential one. In a definition, the corresponding defect consists in defining a being by a feature which belongs to it only accidentally.
So for example, “— wanders off in the middle of the road” is a relevant definite description, allowing unambiguous reference to a dog, but not a defining feature of « dog”.

All the same, “— is a good time for having a nap” is not a defining feature of “afternoon”, S. Two-term Reasoning.

2. The ad accidens counter-argument

The charge of committing the fallacy of accident is possible only if the accuser can refer to a solid and stabilized categorization, corresponding to a set of essentialist definition, S. Definition (1). In ordinary speech,  the accusation of committing a fallacy of accident is just a counter-argument, which opens a stasis of definition and can itself be defeated.

The ethical value of a profession is evaluated on the basis of an examination of the moral worth of its values and practices. In a classical democratic regime, a politician can be honest or dishonest without ever ceasing to be a politician. Dishonesty is not a necessary condition for becoming a politician; it is an accidental feature; “he is an honest politician” is not an oxymoron, “he is a dishonest politician” is not tautologically true. For those sharing this vision of things and people, characterizing political activity as an intrinsically dishonest activity, is committing the fallacy of accident. The person blamed for committing the fallacy might retort that the argument is not based on any transcendental organization of things, but on an inductive generalization, from “a number of politicians we all know very well”; or on the actual structural condition of our political system.

The argument from the opposite, (or a contrario) argument plays with the essential vs. accidental character of the differences between two categories of beings, “boys can go out at night, so girls should not go out, well, you know, girls are different from boys”. It is refuted by demoting the difference from essential to accidental. The same strategy applies to the distinctions between the defining features of a fact, and its circumstantial, contextual characteristics.

Dissociated from the strict Aristotelian ontology, the “essence vs. accident” opposition corresponds to the distinction between central traits and peripheral traits, and, in everyday life, to the distinction between the important and the incidental.

Ultimately, in the absence of backing by an accepted ontology, the so-called fallacy of accident functions as a refutation arguing from the incidental nature of an element, and finally corresponds to a strategy of minimization of the disputed character.

Lat. abductio, “action of taking”, by an outwardly directed movement (see infra, meaning 2).

1. Abduction as inference from facts to hypothesis

The concept of abduction was introduced in modern philosophy by the philosopher Charles Sanders Peirce. According to Peirce, there are two kinds of inferences: deductive inference and abductive inference or abduction. Abduction starts from the observation of a fact “contrary to what we should expect” Peirce ([1958], § 202), that is to say, a fact that does not fit into an available explanatory system. Abduction is a kind of inference by which one proposes a hypothesis accounting for this fact.
This hypothesis is not the product of the application of a “discovery algorithm”, but the fruit of a creative process, “abduction is, after all, nothing but guessing” (Peirce [1958], § 219).

Abduction is not an issue in logic, but rather a scientific method (id., Chap. 6). Scientific work consists in proposing, on the basis of facts, plausible hypotheses “suggested” by these facts. Abduction is the first step in this process.
The practice of abduction is not guided by logical rules but by general principles, such as the principle of exclusion of so-called metaphysical hypotheses, that is to say, hypotheses which would have no experimental consequences, or the principle according to which every fact has an explanation: an abducted hypothesis is interesting “if it seems to make the world reasonable” (id., §202).

Unlike abduction, which starts from facts in search of theory, the Peircian deduction starts from a theory in search of facts; that is, it seeks to identify the crucial experimental consequences of a hypothesis.

Much more than a form of deduction or induction, argumentation should be seen as a form of abduction: because the light is on, “I abduct”, I make the hypothesis, that there is someone in the room; but this hypothesis still needs to be checked, S. Probable, Plausible, True.

Woods redefines abductions as “responses to ignorance-problems. An agent has an ignorance-problem in relation to an epistemic target that cannot be hit by the cognitive resources presently at his command, or within easy and timely reach of it” (Woods, 2009; Gabbay & Woods, 2005). The study of argument as an abductive process has proved especially fruitful in the fields of medicine, science and law (Walton 2004).

2. Abduction as reduction of uncertainty

In its Peircian sense, abduction is a kind of inference by which one arrives at a hypothesis accounting for this fact. Aristotle defines abduction as a kind of dialectical syllogism (Aristotle, PA, II, 25), whose major premise is true, the minor just probable, and, consequently, the conclusion also probable. The conclusion alone, without the minor, is more improbable than the minor. The minor therefore strengthens the relative acceptability of the conclusion. This situation recalls the Ciceronian definition of argumentation, S. Argumentation (I).

For example, if the question is: “can virtue be taught?” we can reason as follows:

A true premise: it is clear that science can be taught.
A doubtful premise: virtue is a science.
Conclusion: virtue can be taught.

Though uncertain, the veracity of the second premise is still less in doubt than the conclusion “virtue can be taught”. This second premise may therefore serve as an argument for the conclusion. We find this montage in speeches such as:

Citizenship can be taught.
Citizenship is essentially a set of social knowledge and practices.
Knowledge is being taught and all practical skills can be improved by teaching. So, citizenship can be taught.

Argument functions “for want of better”. Reduction of uncertainty serves to modify relevantly the epistemic status of a belief. This is a logic not of elimination but of reduction of doubt and uncertainty, S. Default reasoning.

Lat. exemplum, “example”.

In law, the label ab exemplo refers to an argument that interprets the law according to:

1. A previous case, S. Precedent.
2. A traditional interpretation, “the doctrine generally accepted” (Tarello, quoted in Perelman 1979, p. 59).

The argument ab exemplo is therefore distinct from the argument from example.

Some argument schemes are designated by Latin labels, S. Ab —; Ad —; Ex —. This entry lists the labels using the Latin preposition a / ab.

The same Latin preposition has two forms, a or ab: in general, a is used before a noun beginning with a consonant (a contrario argument), and ab before a noun beginning with a vowel (ab auctoritate argument).

1. The construction

In classical Latin, the a / ab preposition means “separation; away from” and governs the ablative case. Grammatically, ab / a introduces only a circumstantial clause of a verb, indicating the origin. This means that the Latin construction “argumentum ab + N” is to be interpreted as elliptical for “argumentum [ducetur, “drawn”] ab [“from”] N”. Latin texts regularly use expressions of this type, Cicero for example, wrote in the Topics:

cum autem a genere ducetur argumentum (my emphasis) (IX, 39; p. 411);

that is “when, however, an argument is drawn from genus”. Genere is the ablative case of the noun genus; the construction is “argumentum [ducetur] a genere”, “argument [provided by, taken] [from] the genus”. Similarly, the rhetoric Ad Herennius suggests that, in order to amplify the charge, the orator has to look first for an argument drawn from authority:

primus locus ab auctoritate sumitur (my emphasis) (Ad Her., II, 48; p. 147);

that is “the first commonplace [primus locus] is taken [sumitur] from [ab] authority [auctoritate]”. Auctoritate is the ablative case of auctoritas, “authority”. Locus means literally “place”, and is taken here metaphorically as “inferential commonplace” or “argument scheme”, S. Topos, Topic Commonplace.

2. List of the “ab (a) + N” arguments

The set of “ab / a + N” arguments belongs to the original stock of Latin argument labels; its core is drawn from the Ciceronian typology, passed on to the Middle Ages by Boethius, up to modern times S. Collections (2).

In stark contrast to the list of “ad + N” arguments (S. Ad — Arguments), the following list contains no label referring to feelings or subjective beliefs.

Table
First column: Latin name of the argument
Second column:

• Meaning of the word(s) (based on Gaffiot).
• (When necessary a word-for-word translation)
• Reference for the corresponding entry

The a / ab arguments constitute the original stock of arguments whose core is taken from Cicero’s typology, S. Collection (2). From Aristotle to Boethius

As opposed to the ad  arguments, we notice that these labels never refer to emotions or subjective beliefs.

The ad  arguments are clearly arguments and not fallacies. In other words, when using the label “ad + N” argument we take the perspective of the proponent, who produces and puts forward the argument, not from the perspective of the opponent whom the argument will impact and who will reject it.

A repugnantibus, lat. repugnans “contradictory; resistant, contrary, incompatible”.
Repugnant meaning “disgusting” is also derived from this source, but the argument a repugnantibus is not the “argument of disgust”, S. Emotions.
The meaning of Lat. repugnans in a repugnantibus is closer to “revolting, unacceptable”, the second meaning of Eng. repugnant.

1. In Cicero’s Topica, the a repugnantibus argument is based on logically “contradictory” things (Cicero, Top, XII, 53; p. 420).
In her translation of Boethius, Stump translates a repugnantibus as “from incompatible” (Boethius Top. p. 64), S. Contradiction; Opposites.

This logical a repugnantibus argument is based on contradiction, whereas the ad incommodum argument involves consequences subjectively unacceptable to the speaker, either from a material or a moral point of view, S. Pragmatic argument.

2. Bossuet defines the a repugnantibus argument as a contradiction between act and speech: “your conduct does not suit your speech” ([1677], p. 140), which corresponds to the third type of ad hominem argument, S. Ad hominem.

Lat. comparatio, “comparison”.

The label “argument a comparatione” refers to two argument schemes:

— Most often, to the argument by comparison. S. A fortiori.

— Sometimes to the argument a pari.

 Ang. Uncertainty of meaning

1. Le sens dans les langages logiques et dans le langage ordinaire

Les langages logiques, formels et scientifiques se distinguent du langage naturel par leur univocité. À chaque chaîne signifiante (terme ou expression), simple ou complexe, correspond une signification (interprétation) et une seule. De telles chaînes ne connaissent ni le vide de sens (le non-sens), ni l’obscurité, ni le flou (le vague), ni l’ambiguité, ni la multiplicité des sens (ambiguïté), ni les variations de sens dans un discours comme dans domaine.

Dans le langage ordinaire, l’interprétabilité des chaînes signifiantes n’est pas garantie. Une chaîne signifiante peut être :

— Vide de sens, ou ininterprétable (non-sens).
Dans le cas le plus général, il est impossible d’attribuer au segment linguistique un sens quelconque. On ne lui trouve pas de paraphrase satisfaisante  (acceptable dans ce contexte). Le texte est totalement obscur, il pose un défi interprétatif, il est inexploitable par le récepteur.

— Obscure. Il est difficile de formuler la moindre interprétation.
Un texte énigmatique n’est pas un texte obscur, dans la mesure où l’énigme a une clé, qui peut éventuellement être trouvée au terme d’un cheminement interprétatif.
La coexistence dans un même discours d’orientations incompatibles est une cause majeure d’obscurité pragmatique.

— Floue ou vague. Il est possible d’attacher à la même chaîne signifiante  plusieurs interprétations également douteuses et discutables.
On parle de flou et de vague à propos de phénomènes limites qui apparaissent particulièrement à propos de la catégorisation et de la définition.
Le vague du discours peut être également lié aux questions de généralisation et de particularisation.

— Ambiguë. La  chaîne signifiante est ambigüe si on peut lui plusieurs interprétations nettement distinctes et incompatibles. L’interprétation hésite entre deux ou plusieurs sens possibles pour le même segment.

— Instable. Le sens d’une même chaîne peut varier ou s’obscurcir,  dans un même discours, V. Objet de discours.

Globalement, ces cinq caractéristiques — non-sens, obscurité, flou, ambiguïté, instabilité — opposent le langage scientifique, qui est le prototype du langage transparent, au langage naturel qui comporte nécessairement une part d’opacité.
Si l’on définit l’activité de raisonnement à partir du raisonnement logico-scientifique, alors l’incertitude du sens dans le discours ordinaire fait apparaître le langage naturel comme un mauvais milieu particulièrement peu favorable au développement du raisonnement.

2. Exploitation argumentative de l’incertitude sémantique

Le sens d’un discours est le produit d’une activité rhétorique d’expression et d’une activité herméneutique d’interprétation. Le sentiment d’incertitude du sens, peut avoir sa source  dans l’incertitude de l’expression ou dans celle l’interprétation.
Ce sentiment d’indétermination se matérialise par un jugement porté par le récepteur. Comme le jugement de clarté, il peut varier avec les récepteurs.
Dans le cas de discours argumentatifs, le jugement d’incertitude porté sur un discours sert à le réfuter.  Le discours cible est invalidé sur le plan logique et rejeté sur le plan interactionnel, V. Destruction du discours. On lui dénie toute pertinence pour l’échange en cours. Comme tous les jugements, le jugement d’incertitude demande donc à être justifié.
Dans certains genres de discours et d’interaction, le sentiment d’incertitude peut être vu, à juste titre, comme une richesse stimulant l’interprétation. Ils exploitent positivement ce que le discours argumentatif rejette comme fallacieux.

L’interprétation d’un discours tient compte du genre et du type d’échange dans lesquels entrent ce discours, et avant tout de son contexte immédiat, l’échange auquel il apporte une contribution. On peut réfuter une accusation d’indétermination en montrant que l’indétermination est levée par la prise en compte d’un ou plusieurs de ces éléments.

Le dialogue collaboratif joue un rôle essentiel dans la levée de l’indétermination ou de la sous-détermination, lorsque le discours n’atteint pas le niveau de pertinence requis par l’échange.