CONSENSUS UNIVERSALIS
Consensus universalis is the general agreement of human thought concerning factual truths and first principles of immediate evidence, or even concerning certain derived truths, particularly of an ethical-religious order. That such a consensus exists is itself an undeniable fact: amid the continuous variation of human opinions, mentalities, tastes, and tendencies, and despite profound historical upheavals in the values of thought and life, human reason in its original spontaneity always finds itself in conformity with itself in its fundamental judgments of truth and goodness.
The reason for this fact, which fideism (T. Reid and his school, F. H. Jacobi) attributes to an obscure instinct of nature, must instead be sought, as St. Thomas expresses it (*Summa Theologica*, I-II, q. 94, art. 2), in the fundamental inclination of spiritual nature toward the good that is proper to it, namely truth, and thus also in the natural capacity to attain II. The *sensus naturae communis* is nothing other than this natural inclination or tendency; and if one wishes to speak of instinct in the sense of a disposition inherent in nature, it is an instinct that is not lacking in a certain self-awareness, in the light and certainty of intellectual knowledge—even if the objective reasons that determine it may remain shrouded in obscurity.
The consensus universalis thus understood must not be confused with the common persuasions of various kinds, often erroneous, that sometimes accompany, even for the duration of historical epochs, the consciousness of peoples and civilizations, and that originate in particular factual circumstances, traditions, or environments—not certainly in the pure and spontaneous exercise of reason.
In ancient philosophy, consensus universalis was already considered an argument for certainty. Aristotle: *"Quod omnibus verum videtur, hoc dictum esse"* (*Eth. Nicom.*, X, 2, 1173 a); Seneca: *"Multum dare solemus praesumptioni (προσχέσεις) omnium hominum; apud nos veritatis argumentum est aliquid omnibus videt"* (*Epist.*, 117); Cicero: *"Omni autem in re consensio omnium gentium lex naturae putanda est"* (*Tusc. Disput.*, I, 13); *"De quo autem omnium natura consentit id verum esse necesse est"* (*De nat. deor.*, I, 17). In the last century, F.-R. de Lamennais (v.) elevated consensus universalis, the "general reason," to the supreme criterion of certainty, to which every affirmation of individual reason should conform in order to emerge from the mores of doubt and rediscover truth: *"The common sense is the rule of every individual reason"*; *"without it there is neither certainty nor truth nor reason"* (*Defense de l'essai sur l'indifférence en matière de religion*, Paris 1821, pp. 571, 625).
Against this excessive evaluation by Lamennais, Scholastic criteriology recognizes in consensus universalis, with regard to certainty, a positive but not primitive value. First, it is necessary to distinguish consensus universalis as it pertains to truths about facts and principles of immediate evidence, or instead to complex and derived truths: in the first case, it may claim an apodictic value not so much because it is a universal fact, but rather because of the theoretical presuppositions that the fact implies—namely, the very value of reason and the objectivity of its fundamental laws. But insofar as it concerns derived truths, for example, the existence of God or the immortality of the soul, the agreement of the greater part of men has only the value of confirmation and more or less consistent probability, on which philosophy, which sustains and justifies itself only through its self-control, cannot in any way rely. In any case, consensus universalis cannot absolutely be taken as the first foundation of certainty, which must be established not on authority but on the evidence critically attained by thought in the reflective examination of itself and the totality of human experience.