Fallacies as Sins of the Tongue

When taking sides truth and rationality, fallacy theory calls for a criticism of language and speech as vectors of error and deceit, S. Evaluation; Norms. Other cultures gave other foundations to the criticism of speech. Reconstructing the history of the “sins of language” in the Middle Ages, Casagrande & Vecchio (1991) have demonstrated the link between speech and sin. The issue then was not to build a rational discourse, but a sinless, “impeccable” discourse, if not a holy one. The nature of the misconduct has shifted: what was declared sinful in the name of religion is now considered to be fallacious or sophistical in the name of rationality. Whether sin or fallacies, salvation of the soul or rational guidance of the mind, it is always a matter of regimenting verbal behavior, disciplining one’s speech and pen.

Casagrande and Vecchio synthesize data from various medieval treatises into a list of fourteen sins. This list can be widely interpreted in terms of misleading interactional argumentative behaviors. These sins-fallacies intend to rule the interaction in a religious context where hierarchy and valorization of authority occupy a central position, S. Politeness.

Making a connection between fallacy theory and “sins of the tongue” is not indulging in any kind of derisio, neither to one nor to the other party. This connection, on the contrary, is intended to show how deep the anthropological roots of discourse criticism are.

1. Sins against truth

1.1 Lying

Telling the truth, all the truth and nothing but the truth is certainly a basic commitment for a non-fallacious debate. Lying, as saying something false to someone who has no access to truth, is a sin in the system of theological norms, and a fundamental violation of Grice’s cooperative@ principle S. Manipulation

1.2 Aggravated lying: perjury and false testimony

In judicial rhetoric, oath and testimony, two major instruments to establish the truth, are considered to be non-technical proofs, S. “Technical’ and “Non-technical” evidence. Their violation corresponds to two aggravated lies, the sins of perjury, perjurium, and false testimony, falsum testimonium.

2. Six sins of interaction

2.1 Against disputes

Rivalry, conflict, fight (contentio), and discussion (disputatio) are names denoting the very activity of disputing. It can thus be said that arguing is potentially considered sinful at its very core. It is the sin of the intellectual monks, and no doubt, that of Abelard. The passage from the peccaminous to the fallacious is explicit in the Port-Royal Logic, in which the excessive love of dispute, the spirit of contradiction, is condemned as a sophism of self-esteem (n°6 and 7), a fundamental feature of the character of “those who contradict” (Arnauld and Nicole [1662], p. 272); S. Fallacies (IV). The debate is subject to a moral imperative: the contradiction must be genuine, not “malignant and envious” (ibid.) – or, to move on to judicial pathology, querulous. Such a debate might be legitimately declined.

We then discern two families of sins of interactional positioning, on the one hand, the sins “towards the other”, the partner with whom we argue (§ 2.2), and, on the other hand, the sins committed “towards oneself” as a speaker (§2.3). In both cases, it is a question of banishing illegitimate treatments of the partners of the interaction, S. Politeness.

2.2 Three kinds of sins towards the partner

Undue negative treatment: offensive remarks (contumelia) or slander (detractio). These two sins are a form of personal attacks, or ad personam fallacies. The derisio, as a contemptuous mockery, could be associated with this fallacy, S. Ad hominem; Dismissal.

Negative treatment under the cover of the positive: this is the mechanism of refutation by self-evidence as implemented through irony, ironia. This intention to hurt the other is dealt with only laterally in contemporary theories of irony.

Undue positive treatment: flattery (adulatio), and even simple praise (laudatio). These two sins involve the same interactional mechanisms as found in the fallacy of modesty@, ad verecundiam, where the speaker humiliates himself unduly before his partner. Adulatio and laudatio encourage pride, and pride is a sin. Logic, religion, and politeness speak with one voice, S. Modesty; Politeness.

2.3 Two kinds of sins against oneself

Undue positive treatment, in other words, boasting, iactantia. This ethotic sin stigmatizes the projection in the discussion of an overly positive self-image, S. Ethos. According to politeness theory, the iactantia sins against modesty.

Undue negative treatment is the symmetrical sin of the sin of undue positive treatment of the partner, S. Modesty. The taciturnitas, sin of the person who keeps silent when he should speak, can be related to the ad verecundiam fallacy in which “human respect” inhibits criticism.

4. Murmuring: a sophism of insubordination

A person who complains against authority commits the sin of murmur (murmur), S. A fortiori. A person who refuses to yield to the force of the best argument having little to oppose to it, save an intimate conviction or sense of justice, is guilty of the same kind of fallaciousness, S. Dissensus; Rules. Insubordination is irrational, illegal, peccaminous.

5. The sin of eloquence

Eloquence, seen as an abundance of words, amplification, repetition, magnification, is the source of all fallacies, S. Verbiage. The same evaluation should apply to idle speech (vaniloquium), as well as to chatter (multiloquium).

6. Flaring into a passion: ad passiones

Some remaining sins are difficult to connect to the problematic of fallacies, perhaps because they directly involve the relation to the sacred: the prohibition of obscene words (turpiloquium), blasphemy (blasphemia) and the curse (maledictum). Nonetheless, these sins can have an ad personam function. Above all, they have an emotional import, so they certainly relate to the ad passiones group. Blasphemy is anger against god, and cursing, anger against the other; obscene words can be used to support many passions, including insulting.


To sum up, the theory of the sins of language is a critical theory of discourse taking into account:

— The “non-technical” problems of lying or attesting the truth.
— The spirit of the discussion.
— The relative interactional positions of the participants.

7. The “rules of the devil”

This list of fallacies-sins does not mention violations of logical rules, such as the assertion of the consequent (confusion of necessary and sufficient conditions, S. Deduction. One would think that it is because the logical domain, by nature escapes the religious norm. In the Muslim tradition, however, one can find the vocabulary of sin applied to paralogisms, which Al-Ghazali considers as “rules of the devil” (Bal., p. 171; Deg.). A medieval exemplum also puts the logician into hell, assimilated to the sophist, S. Exemplum.