CERTAINTY. — From cernere, to sift, discern, certainty is, in the proper sense, the mental state of firm adherence
to a proposition. St. Thomas: «certitudo proprie dicitur firmitas adhaesionis virtutis cognoscitivae ad suum cognoscibile»; «certitudo nihil aliud est quam determinatio intellectus ad unum» (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 the objects of knowledge and of the conditions on which it is founded.
The division of certainty into metaphysical, physical, and moral, common since Leibniz (Now. ess., IV, 6, 13), is called by Balmes respectively absolute, natural, and ordinary. Metaphysical certainty is that founded on the absolute necessity of the essential laws of reality (the whole is greater than the part); physical certainty is that founded on the stability and constancy of the laws of nature (tomorrow the sun will rise); moral certainty is that founded on the ordinary validity of the practical laws of life (war makes men worse). It is evident, however, that in the latter case one cannot speak of certainty in the proper sense, since there is lacking an objectively and universally valid foundation sufficient to determine thought with assurance. The expression “moral certainty” also has several other meanings. At times it is taken as a synonym for maximum probability; often it designates practical certainty concerning the morality of a given action, a certainty not necessarily linked, as in the case of a doubtful law, to theoretical evidence. By the expression “ethical certainty” one today frequently means the particular condition characterizing the perception of moral values, attributed not so much to evidence of a conceptual order as rather to intuition or moral feeling.
As appears from its notion, certainty is a subjective modality of knowledge; nevertheless, one also speaks of objective certainty as opposed to subjective certainty, in order to distinguish legitimate certainty founded on truth from the purely psychological state of secure persuasion that sometimes accompanies error. Finally, a distinction is made between spontaneous certainty, proper to reason in its natural and prescientific exercise, and reflective certainty, the fruit of an explicit becoming-conscious on the part of thought of its own affirmations and of the motives grounding them. In practice, however, this distinction is not as sharp as it may appear, 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 spirit, understood in the proper sense indicated above, are and must be objective, that is, inherent in the object of judgment: thought can remain with absolute assurance in an object of knowledge only insofar as the latter manifests itself to thought in the light of its truth, that is, of its inner necessity.
A purely subjective state of persuasion can certainly arise from various and manifold causes, both internal and external, including desire, passion, and any kind of psychological consonance; but 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 in relation to facts and states of consciousness, and logical evidence of the connection of concepts with regard to judgments of an ideal order. In saying this, while rejecting the fideistic and voluntaristic position (Reid, Jacobi, Jouffroy, Goblet, etc.) that assigns the determinants of certainty to the realm of instinct and will, one does not exclude the possibility that certainty may often mature on the basis of a complex of psychological dispositions and coefficients in which, besides the intellect, will and the heart also play their part. This applies especially — to say nothing of aesthetic certainty, which is essentially alogical and therefore belongs to feeling — faith (v.), where only an extrinsic evidence is possible, based on the certainty of revelation and divine infallibility. Today, however, outside scholastic terminology, the persuasion of faith is generally designated simply by the term faith or belief (v.), while the name certainty is reserved for persuasion of an intellectual order derived from intelligence.
At various points in the history of thought, the question has been raised whether man can truly attain certainty. Evidently, the issue does not concern spontaneous certainty, a universal fact of immediate
experience, but reflective certainty, absolutely valid in the philosophical sphere and as a matter of principle. The skeptical challenge (v. SCETTICISMO) draws its strength from the perennial and apparently insuperable crisis of truth in the human mind. But the answer in the affirmative admits of no doubt, provided thought turns back upon itself and becomes conscious of the absolute values it possesses: in its varied and rich experience of itself, thought holds in its grasp the firmest certainties, superior and impervious to every doubt. In these first certainties, grasped in self-consciousness and immediately translated into certainties of principle, lies the surest foundation for a general affirmation of certainty in the field of philosophy and life (v. CONOSCENZA; CRITERIO; EVIDENZA).