H. P. Grice's Desideratum of Conversational Candour

Alexander of Hales distinguishes a duplex veritas as a pendant to a duplex falsitas, the falsitas dicti, the falsehood of what is said, and the falsitas dicentis, the “falsehood” of the speaker. As a result, according to Bonaventure, the outer speech can be considered in two modes: in comparison to the thing, the discourse (sermo) is said to be verus (as opposed to falsus) when there is adequation between the thing and the discourse (adaequatio rei et sermonis); but in relation to the intentions of the speaker, the discourse is said to be verax (as opposed to fallax) when there is adequation between the discourse and the intention (adaequatio sermonis et intentionis). As we see, the formula follows the wording of the truth as adaequatio rei et intellectus. The terms verax and mendax can also describe a discourse as well as a speaker. But in Thomas Aquinas it would seem that verax can only be applied to the speaker (the translation as “sincere” is not precisely correct, in that the term is simply “[he] who says the truth straightforwardly”). He thus very clearly distinguishes, in the line just described, between logical truth, by which something said is true (adaequatio intellectus vel signi ad rem intellectam et significatam), and moral truth, by which someone is said to be verax, and it is this latter that constitutes a virtue and whose infraction results in a lie (Summa theologica, 11, 11, q. 109, a. 1). The reflections on lying reveal a development that will profoundly modify Augustinian thought. The first underscores the responsibility of the speaker in regards to his use of language; the others relate to the speaker’s responsibility to the other. The Augustinian definition refers to “intentio fallendi,” an intention to deceive, while in fact it results from a “determination to speak falsely,” as Alexander of Hales emphasizes, by reformulating it thus: “Falso vocis significatio cum voluntate falsum enuntiandi,” a false utterance with the intention of uttering falsehood) (Summa theologica, p. 402, § 399). The speaker is expected to know the rules of language as fixed by convention. If he speaks in a way that does not reflect his intentions, or speaks in equivocal terms, or in formulae that are open to different interpretations from the intended meaning on the part of the listener, he is at fault. Thomas Aquinas puts this reformulation together in proposing an analysis of lies in three parts: (1) falsehood in matter, when the utterance is false; (2) falsehood in form, or the desire to utter the false (voluntas falsum enuntiandi); (3) falsity in effect, or the intention to deceive (intentio fallendi). Since it is beyond man’s capacities to fully say or know the truth, the lie can only be defined as a voluntary deviation from the truth (Summa theologica, d. 39).