Ab — Arguments (A Contrario…)

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.

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
Latin name of the argument


• Latin term(s) and their English equivalent(s)
• (Global translation)
• Corresponding entry/ies.
ab auctoritate Lat. auctoritas, “authority” — S. Authority; Modesty
a carcere Lat. carcer, “jail” S. Threats — Promises ; Threat; Emotion.
a coherentia Lat. cohærentia, “coherence, consistency” – S. Consistency.
a comparatione Lat. comparatio, “comparison; confrontation”
S. Comparison; A fortiori; Analogy
a completudine Lat. completus, “complete” — S. Completeness
a conjugata Lat. conjugatus “belonging to the same family”
S. Related Words
a contrario (sensu)
(or: ex contrario)
Lat. contrarius “opposite, contrary” — S. Opposites
a consequentibus Lat. consequens “close; what logically follows”
S. Circumstances; Consequences.
a fortiori
a fortiori ratione
Lat. a fortiori ratione, “for a stronger reason”; ratio, “reason”; fortior = fortis + higher degree comparative “stronger” — S. A fortiori
a generali sensu Lat. generalis, “general”; sensus “meaning, point of view” —
S. Generality of the law
a genere Lat. genus, “genus” — Argument from genus
S. Genus; Classification; Definition; a pari
a pari Lat. par, “equal, same” 
— S. a pari
a posteriori Lat. posterus, “which comes after” —S. A priori; A posteriori
a priori Lat. prior, “the first of two, superior” — S. A priori; A posteriori
a repugnantibus Lat. repugnans, from repugnare “contradictory; contrary; incompatible” — S. A repugnantibus; Opposites.
a rubrica Lat. rubrica, “title of the section (law)” — S. Title
a silentio Lat. silentium, “silence” — S. Silence.
a simili Lat. similis, “resembling, similar” — S. Analogya pari
ab absurdo
[or: ad absurdum]
Lat. absurdus, “absurd” — S. Absurd.
ab adjunctis Lat. adjuncta, “attached to” — argumenta ex adjunctis ducta, arg. from circumstances — S. Circumstances.
ab antecedentibus Lat. antecedens, “preceding” — S. Circumstances.
ab consequentibus Lat. consequens, “following” — S. Circumstances; Consequences.
ab auctoritate
ad auctoritatem)
Lat. auctoritas, “authority” — S. Authority.
ab enumeratione
Lat. enumeratio “enumeration”; pars, “part”
arg. from enumeration of parts
S. Composition — Division; Case-by-case; Definition.
ab exemplo Lat. exemplum “example” S. Example; Exemplum; Precedent.
ab inutilitate Lat. inutilitas, “useless, dangerous” — S. Superfluity
ab utili Lat. utilitas, “useful, beneficial” — S. Pragmatic argument


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.