“Nihil probat, qui nimium probat.”
Why is it that we humans of the 21st century are still blinded by the illusion of the homo oeconomicus when we are forming an opinion? What exactly is conviction – true rationality or mere illusion?
It would be prudent to look deeper into rhetoric and philosophy in order to analyse the term “conviction” and its varied meanings properly.
Conviction (πίστις / convictus, fides, probatio) will be determined here as a firm belief or fixed opinion that someone formed about a specific issue. It is to be distinguished from knowledge (facts and absolute truth as a true conviction), certainty (objective knowledge), belief (intuitive, subjective knowledge) and cognition (founded knowledge that results from reasoning).1
In Phaedrus (272d-e) Plato assumes a big opposition between truth (ἀληθεία) and conviction (πιθανόν) which is induced by rhetoric. He thereby introduces the antique schism of philosophy (sapientia) on the one hand and rhetoric (eloquentia) on the other. This dramatic contrast is still relevant in rhetoric to this day even though Cicero tried to mediate in his De oratore. Philosophy lays claim to wisdom as the absolute truth and real being of a thing whereas rhetoric lays claim to the power of persuasion and credibility.
According to Aristotle, rhetoric is the faculty (δύναμις) of discovering the compelling means of persuasion in every issue that is to be dealt with.2 It is an ability to find the right words for persuading people.3 Persuasion is a process in which arguments (induction or deduction, enthymeme, the so called πίστεις ἔντεχνοι) or artless proofs (πίστεις ἄτεχνοι) such as witnesses or documents bear great appeal. Rhetoric is closely related to dialectic and strives from within it in Aristotle’s view. Even though the enthymeme as a rhetorical syllogism is important in formal logic, it is the ethos of the orator that is the most compelling means of persuasion.4 This is due to the fact that the persuasive process is being directed towards the audience5 and is rooted in the credibility of the orator and the probability of the issue at hand. In his view, persuasion is successful if the matter at hand is either probable (εἰκός) or convincing (πιθανόν).6
Cicero translates εἰκός to Latin as veri simile (in Latin) and πιθανόν as probabile. Both concepts address the problem of cognitive uncertainty in reasoning. Veri simile seems to be a philosophical term etymologically as it means “similar to the truth” and thereby refers to an objective truth. Probabile however seems to be a rather rhetorical term as it is translated with “probable” and stands for a subjective truth in any rhetorical situation.7
A persuasive speech of the perfect orator has to be lucid, brief and veri simile in Quintilian’s mind.8 He turns his interest to taxonomies of proof and reminds his readers that both true things and fictitious things have to be proven.9 For him, rhetoric is a virtue and a science (bene dicendi scientiam)10.
Conviction in philosophy possesses a rationality that is justified by reliable methods and proven arguments. This vesting continues to be upheld11 even though Plato’s ideal of a true conviction12 as knowledge (ἐπιστήμη) via λόγος cannot always be guaranteed.
Rationality is loosely defined in rhetoric as it also allows emotional means within persuasion. Argumentation is not necessarily based on the truth but on the probable (defined as that which comes closest to the truth). Epistemic sentences rather than probable reasons will suffice in rhetoric.