Lat. ex datis, datum, “gift, present”.

The label “ad auditorem argument”, lat. auditor “listener” is used by Schopenhauer ([1864], p. 43).

The ex datis argumentation is not based on facts or experience, but on what has been admitted, “given”, or conceded by the interlocutor, the audience or the adversary. The arguer reasons, “from what has been granted” (Chenique 1975, p. 322). The ex datis argumentation is sometimes called ex concessis^@ (ibid.).

Like the ad hominem^@ argument, the ex datis argument is based on the beliefs of the audience. While the ad hominem argument exploits these beliefs to rebut the whole system, the ex datis argument exploits them for confirmation purposes only. Good knowledge of the audience’s character is important to argumentative rhetoric, because it provides the orator with a great reserve of such ex datis premises, S. Ethos.

If the interactional framework does not allow the revision of beliefs, this data cannot be questioned, and the conclusions based upon it are irrefutable in this context. From this data, the arguer concludes positively, “besides, you yourself sayit!”. Consider the issue, “Should we take military action in Syldavia?”:

You admit that the Syldavian troops are poorly trained and that the situation will soon be out of control;
and that the unrest in Syldavia may extend to the region;
we agree that this extension would threaten our security;
and no one denies that we must intervene if our security is threatened.
So, you should join us, the camp of the people who are in favor of a military intervention in Syldavia.

This strategy of argumentation has something to do with religious confession and philosophical maieutic. The listener is invited to assume the truth of his or her beliefs, that is the conclusion that he or she does not dare to draw, or is unable to express because of some intellectual or moral inhibition.

The ex datis argument scheme calls for a foundational and an ethical criticism. According to the foundational principles, to be valid, an inference must be based on true universal premises, whereas any ex datis argumentation is misleading because its premises are based upon local beliefs only. As the ex datis argument is the typical form of rhetorical argumentation, all such rhetorical arguments must be condemned.

From an ethical point of view, and unlike the logician arguing for what is, or what he truly believes to be true, the party putting forward an ex datis argument does not necessarily endorse and support the premises and rules borrowed from the audience. This is why the ex concessis argument may end up as a trap. People are generally expected to take responsibility for what they say, so the audience in good faith will normally allocate to the arguer the beliefs he or she argues from, even if the speaker only advances them ex concessis. Yet, if this arguer is better informed than the audience and knows that P is true (or false), whereas the listeners believe that P is false (or true); or if he or she has reliable information unknown from the audience, and takes into account only what the audience believes and knows, then, to say that the argument is ex datis, ex concessis, ad auditorem… is simply to say that the orator lies and manipulates the audience. S. Refutation; Manipulation.

In philosophy, Kant draws a distinction between ex datis knowledge based on experience, and ex principiis knowledge deduced from the first principles. History is the prototype of knowledge ex datis, philosophy and mathematics prototypes of knowledge ex principiis. Mere ex datis knowledge would be only a compilation of data. Extending the Kantian meaning, one might think that the ex datis argumentation is based on experience, “on the substance, on things themselves”. This interpretation would make ex datis an equivalent of the ad rem, to the matter^@ argument, and this does not seem to be the case. The use of the expression ex datis in argumentation is distinct from its use in philosophy.