CERTAINTY. — To be compared, weighed, discerned, certainty is, in the proper sense, the mental state of firm adherence to a proposition. St. Thomas Aquinas: “Certainty is properly called the firmness of adherence of the cognitive faculty to its object”; “Certainty is nothing other than the determination of the intellect to one [object]” (In III Sent., dist. 26, II, 4; ibid., dist. 23, II, 2, sol. III).
Certainty admits of various distinctions, especially in relation to the diversity of objects of knowledge and the conditions that ground II.
After Leibniz (Nouveaux Essais, IV, 6, 13), it is common to divide certainty into metaphysical, physical, and moral, which Balmes respectively calls absolute, natural, and ordinary. Metaphysical certainty is that grounded in the absolute necessity of the essential laws of reality (the whole is greater than the part); physical certainty is grounded in the stability and constancy of natural laws (tomorrow the sun will rise); moral certainty is grounded in the ordinary validity of the practical laws of life (war makes men worse). It is evident, however, that in this last case one cannot speak of certainty in the proper sense, since there is lacking an objectively valid foundation universally sufficient to determine thought with certainty. The expression “moral certainty” moreover has several other meanings. Sometimes it is taken as a synonym for maximum probability; often it designates practical certainty regarding the morality of a particular action, a certainty not necessarily tied, as in the case of a doubtful law, to theoretical evidence. Today, the expression “ethical certainty” frequently refers to the particular condition that characterizes the perception of moral values, attributed not so much to evidence of a conceptual order as rather to moral intuition or sentiment.
As appears from its notion, certainty is a subjective modality of knowledge; yet one also speaks of objective certainty, as opposed to subjective, to distinguish legitimate certainty grounded in truth from the purely psychological state of firm persuasion that sometimes accompanies error. Finally, one distinguishes spontaneous certainty, proper to reason in its natural and pre-scientific exercise, from reflected certainty, the fruit of an explicit awareness on the part of thought of its own affirmations and the reasons that ground them. In practice, however, this distinction is not so sharp as it may seem, since an initial reflection is always present wherever one explicitly knows the impossibility of the opposite, as is frequently the case with spontaneous certainty.
The reasons that determine certainty in the mind—understood in the proper sense indicated above—are and must be objective, inherent to the object of judgment: the mind can come to rest with absolute security in an object of knowledge only insofar as that object manifests itself in the light of its truth, that is, its inner necessity.
A state of purely subjective persuasion may indeed arise from various and manifold causes, internal or external, not excluding desire, passion, or any psychological consonance; yet full and conscious certainty is always, in the final analysis, determined by the evidence of being that opens itself to thought in its intelligibility: concrete evidence of intuition with respect to facts and states of consciousness, and logical evidence of conceptual connection with respect to judgments of an ideal order. In this, while rejecting the fideistic and voluntaristic positions (Reid, Jacobi, Jouffroy, Goblot, etc.) that refer the determinants of certainty to the realm of instinct and will, one does not exclude the fact that certainty may often mature upon a complex of psychological dispositions and coefficients in which, alongside the intellect, the will and the heart also play a part. This is especially true—leaving aside aesthetic certainty, essentially alogical and therefore of sentiment—for truths of faith (v.), where only an extrinsic evidence is possible, based on the certainty of revelation and of divine infallibility. Today, however, outside of scholastic terminology, the persuasion of faith is usually designated simply by the term faith or belief (v.), reserving the name of certainty for the persuasion of an intellectual order derived from intelligence.
Repeatedly in the history of thought the question has been raised whether man can truly attain certainty. It is not, obviously, a matter of spontaneous certainty, a universal fact of immediate experience, but of reflected certainty, absolutely valid in the philosophical sphere and in principle. The skeptical challenge (v. skepticism) appeals to the perennial and, it would seem, insurmountable crisis of truth in the human mind. Yet the positive answer admits of no doubt when thought turns back upon itself and becomes conscious of the absolute values it possesses: in the varied and rich experience of itself, thought holds in hand the most solid certainties, superior and refractory to every doubt. In these first certainties actually grasped in self-consciousness and immediately translated into certainties of principle, there lies the surest foundation for an affirmation, in a general sense, of certainty in the domain of philosophy and of life (v. KNOWLEDGE; CRITERION; EVIDENCE).