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The word certitude indicates both a state of mind and a quality of a proposition, according as we say, "I am certain", or, "It is certain". This distinction is expressed in the technical language of philosophy by saying that there is subjective certitude and objective certitude. It is worthy of notice, as regards the use of English terms, that Newman reserves the term certitude for the state of mind, and employs the word certainty to describe the condition of the evidence of a proposition.

Certitude is correlative to truth, for truth is the object of the intellect. Knowledge means knowledge of truth ; and hence we are in the habit of saying simply of a proposition that "it is certain", to express that it is true, and that its truth is so evident as legitimately to produce certitude. Certitude is contrasted with other states of mind in reference to a proposition: the state of ignorance, the state of doubt, and the state of opinion. The last-named signifies, in the strict use of the term, the holding of a proposition as probable, although in common parlance it is loosely used in a wider sense, as in speaking of a man's religious opinions, meaning not his speculations or theories about religious questions, but his dogmatic convictions. Certitude is such assent to the truth of a proposition as excludes all real doubt. Here it is proper to observe a distinction between merely undoubting assent, i.e. the mere absence of doubt, and an assent that positively excludes doubt, an assent with which doubt is incompatible. Thus one may give to a statement in the morning newspaper an undoubting assent and credence, yet readily withdraw that assent if the statement be contradicted in the afternoon papers. Such assent, though undoubting, is not certitude. But there is a kind of assent from which doubt is not only in fact absent but absent of necessity, because such assent and doubt are incompatible. Such is the assent which one gives to the truth that he really exists, and that he feels well or ill, or to the truth of the proposition that it is impossible for a thing in the same respect both to be and not to be, or to the moral law, the existence of God, and the immortality of the soul. Of these truths we are certain, and such assent is properly called certitude. Certitude differs from opinion in kind, not in degree only; for opinion, that is assent to the probability of a proposition, regards the opposite proposition as not more than improbable; and therefore opinion is always accompanied by the consciousness that further evidence may cause a change of mind in favour of the opposite opinion. Opinion, therefore, does not exclude doubt ; certitude does. It has been disputed among philosophers whether certitude is susceptible of degrees, whether we may rightly say that our certitude of one truth is greater than our certitude of another truth. In Zigliara's judgment, this question may easily be solved if a distinction is made between the exclusion of doubt (in which our various certitudes of different truths are all equal, and by which they are all equally marked off in kind from opinion) and the positive firmness of assent, which may be more intense in one case than in another, though in both it be equally true that we are certain. And, in fact, if we examine experience on this point, it is clear that our certitude of a self-evident truth, e.g. of the axioms of geometry, is greater than our certitude of a proposition demonstrated by a long and complex series of proofs, and that our certitude of such a fact as our own existence or our own state of feeling (gladness or health) is greater than our certitude of the existence, for instance, of a republican form of government in this country, though we are certain in both cases. We are more certain when we assent to a truth as certain which falls in with our inclination than when we are forced to a conviction. It should be noted, too, that in the common opinion of theologians there is a greater certitude in divine faith than in any human science.

There are several kinds of certitude. In the first place, it is divided into metaphysical, physical, and moral certitude.

Metaphysical certitude is that with which self-evidently necessary truth is known, or necessary truth demonstrated from self-evident truth. The demonstrative sciences, such as geometry, possess metaphysical certitude. The contingent fact of one's own existence, or of one's present state of feeling, is known with metaphysical certitude.

Physical certitude is that which rests upon the laws of nature. These laws are not absolutely unchangeable, but subject to the will of the Creator; they are not self-evident nor demonstrable from self-evident truth ; but they are constant, and discoverable as laws by experience, so that the future may be inferred from the past, or the distant from the present. It is with physical certitude that a man knows that he shall die, that food will sustain life, that electricity will furnish motive power. Astronomers know beforehand with physical certitude the date of an eclipse or of a transit of Venus.

Moral certitude is that with which judgments are formed concerning human character and conduct; for the laws of human nature are not quite universal, but subject to occasional exceptions. It is moral certitude which we generally attain in the conduct of life, concerning, for example, the friendship of others, the fidelity of a wife or a husband, the form of government under which we live, or the occurrence of certain historical events, such as the Protestant Reformation or the French Revolution. Though almost any detail in these events may be made a subject of dispute, especially when we enter the region of motives and try to trace cause and effect, and though almost any one of the witnesses may be shown to have made some mistake or misrepresentation, yet the occurrence of the events, taken in the mass, is certain.

Father John Rickaby ( First Principles of Knowledge ) observes that certitude is not necessarily exclusive of all misgiving whatsoever (such as the thought of the bare possibility that we may be mistaken, for we are not infallible ), but of all solid, reasonable misgivings. The term moral certitude is used by some philosophers in a wider sense, to include an assent in matters of conduct, given not on purely intellectual grounds of evidence, but through the virtue of prudence and the influence of the will over the intellect, because we judge that doubt would not be wise. In such a case, we know that an opinion or a course of action would be right as a rule, let us say, in nine cases out of ten, though we cannot shut our eyes to the possibility that the particular case which we are considering may be the exceptional case in which such a judgment would be wrong. Other philosophers say that in such a case we are not certain, but only judge it wise to act as if we were certain, and put doubts aside because useless. But it seems clear that in such a case we are certain of something, whether that something be described as the truth of a proposition or the wisdom of a course of action. This certitude might perhaps better be called Practical certitude, since it mainly concerns action. Hence, it is said that in cases in which it is necessary to act, in which great issues are involved, and yet the evidence, when logically set forth, would seem to amount to no more than a higher probability for one course than for another, the standard of judgment, or criterion, is the judicium prudentis viri, the judgment of a wise man, whose mind is unclouded by passion or prejudice, and who has some knowledge derived from experience of similar cases. Such a judgment is totally different from the spirit of the gambler's throw, which is reckless not only of certainty but even of probability.

Certitude is likewise divided into natural certitude (termed also direct, or spontaneous) and philosophical. Natural certitude is that which belongs to "common sense", or the spontaneous working of the judgment, which is common to all men not idiots or insane. This certitude belongs chiefly to self-evident truth and to the truths necessary for the conduct of life, e.g. the existent of other beings besides ourselves, the duties existing between husband and wife, parents and children, the existence of a Supreme Being deserving of reverence. To these and similar truths the mind comes with certitude, without any special education, in the ordinary course of life in human society. Philosophical (or scientific ) certitude is that which results from a process of reflection, upon an analysis of the evidence for and against our convictions, a perception of the reasons which support them and of the objections which may be urged against them, together with an examination of the powers and the limits of the human intelligence. The term natural certitude is sometimes used in another sense, in contradistinction from the certitude of Divine faith, which is supernatural certitude, and which, according to theologians generally, is greater than any degree of certitude to be had in science, because it rests not upon human reason, which is liable to be mistaken, but upon the authority of God, who cannot err. (St. Thomas, Summa, I, Q. i, a. 5.)

A great part of philosophy is taken up with the questions whether certitude is possible, what is the extent of the sphere of certain knowledge, and by what tests or criteria truth may be certainly distinguished from falsehood, so that we may know when we have a right to be certain. A few philosophers in ancient and modern times have, seriously or not, denied the possibility of attaining certitude on any subject whatsoever, and professed universal scepticism. Such are Nicholas of Cusa, Montaigne, Charron, and Bayle, the last of whom aimed at producing the impression that everything is disputable by showing that everything is disputed. Literally universal scepticism is impossible, for it is a profession of knowledge to assert that nothing can be known, and to believe that there can be no belief. It is thus a contradiction in terms. A sceptic should in consistency be sceptical as to his own scepticism ; but no attention would be given to such a sceptic unless as one attends, for amusement, to a jester. Nevertheless, universal scepticism may practically produce pernicious consequences, because its universality is overlooked, and its arguments are viewed as if they applied only to some particular sphere in which the reader (if it so be) is tempted to doubt. Thus, sceptical objections against the principle of causation may be employed against the proofs for the existence of God, while the reader is not warned, and does not remember, that they would equally avail against taking food and sleep for the restoration of strength, or against the anticipation that the sun will rise to-morrow. It should be added that some Christian apologists, in endeavouring to prove the necessity of Divine revelation, have used language differing but little from that of scepticism, to the disparagement of human reason. A noted example is Huet, "Traité de la faiblesse de l'esprit humain" (Paris, 1723).

What is more common than a profession of universal scepticism is a scepticism as to the possibility of philosophic certitude. Many who have no doubt as to natural certitude, or the certitude acquirable by "common sense", the natural, spontaneous action of the unsophisticated mind, regard philosophy as more apt to open questions than to settle them, and to raise objections than to solve them. This seems to have been the position of Pascal, who says: "Reason confounds dogmatists, and nature confounds sceptics "; and, "The heart has reasons of its own which the understanding does not know ". This seems to have been the position also of a very different man, David Hume, who says: "Fortunately since reason is incapable of dispelling these clouds, nature herself suffices for that purpose and cures me of this philosophical delirium" (Treatise of Human Nature, I, 297). He said to a friend who spoke to him concerning the future life and the existence of God : "Though I throw out my speculations to entertain the learned and metaphysical world, yet in other things I do not think so differently from the rest of the world, as you imagine." And he gives his idea of scepticism in a remark upon Berkeley's arguments against the real externality of the sensible world: "That these arguments are in reality merely sceptical appears from this, that they admit of no answer, and produce no conviction; their only effect is to cause that momentary amazement and irresolution and confusion, which is the result of Skepticism." (Inquiry Concerning Human Understanding, ch. xii, note 4.) Kant's system, which denies that the speculative reason can attain to real knowledge, and admits only Practical certitude, and consequently denies the possibility of any system of metaphysical philosophy, is virtually the same view. It is needless to say that, in a philosopher, such a view is self-contradictory. Kant's "Critique of Pure Reason", as well as his other works, was an exercise of the speculative reason. If certitude of knowledge is not obtainable on any subject by the speculative reason, how could he indulge in such positive and dogmatic propositions? If we consider this view of philosophy, as it is held by some men of sense and virtue, who point to the disputations and wranglings of philosophers, the variety of opinions, the number of infidel philosophers, and the general suspicion felt by earnestly religious people, the answer to it is, that this view has some measure of truth, but is a great exaggeration. It is quite true that philosophical inquiries concerning morals and religion, if not conducted with proper moral dispositions, are likely to terminate in doubt. If there be any bias, whether conscious or unconscious, against the obligations of morality and religion, there can of course be only one issue. If the understanding seeks to know everything; if it rejects facts, however well attested, because it does not see how they can be so; if it will accept no truth, however firmly demonstrated, unless the harmony with every other part of a system can be made clear; if the mind makes itself the measure of possibility; if it claims to see through and through the universe, and its origin, and its end; if it refuses to submit to mystery, or to acknowledge that it is limited; and if, because it cannot know everything, it will proudly not consent to know anything, of course with such a disposition philosophizing cannot issue in philosophic certitude. But that is not the fault of philosophy, nor of reason ; and the abuse cannot take away the use, but only be a warning against the misuse of philosophy.

"Methodic doubt ", that is, provisional doubt of every truth, was put forward by Descartes as the proper course for the discovery of truth. This philosopher teaches that in order to be certain of the truth of our convictions we should begin by doubting everything, except one thing: "I think, and therefore I am." He professes to hold that every other truth may be doubted and needs proof. He suggests that we may doubt whether we can discover the truth on any other point whatsoever, for it may appear possibly that we have been created by a malign or mischievous beings who so constituted our mind that we must invariably be mistaken. The Cartesian method is self-contradictory. To make the supposition that possibly the human intellect cannot know the truth, on any point whatsoever, is to assume that this supposition may be true, and that there is such a thing as truth, and that it can be known. To attempt to disprove the supposition, to undertake to show the veracity of the cognitive faculties, presupposes their veracity or power of knowing the truth on some points at least. In fact, Descartes proved the veracity of the cognitive faculties from the veracity of God. The veracity of God, however, is known as the result of a demonstration of some length and complexity; and the undertaking of such demonstration shows a previous belief in the power of the mind to discover the truth. In fact, the very doubt on such a subject is a self-contradiction; for doubt as well as certitude is correlated to truth. To doubt whether a particular view may not be false is to suspect that the opposite may be true. To doubt that the intellect can know any truth is to question whether it may not be true that we are ignorant. But this implies that there is such a thing as truth, and that the truth at least about our own power of knowing, can be discovered. Without such a presupposition, thought cannot be carried on at all. Nor is it a blind presupposition or animal instinct. For in the perception of first principles, or truths evident by their own light, there is implicit the perception that there is such a thing as truth and knowledge. The error in Descartes' method is its exaggeration. It is wise to be on our guard against the prejudices, or opinions, peculiar to a particular time and place, the place of birth or education, the class or party to which our early associations have attached us; but the principles which are self-evident, or which are accepted by the human race, should be exempted from doubt. It must be remembered, too, that the Church teaches that a Catholic cannot without sin entertain doubts against the Faith ; though, of course, he may lawfully doubt whether it is true that a particular doctrine is taught by the Church, or whether he has correctly apprehended what the Church intends to teach, and whether a particular teacher expounds it correctly; or, again, he may investigate the evidences of Christianity and of Catholicism, and may doubt whether a particular argument is valid proof. But the method of doubt, taken as a whole, has been condemned by the Church.

Since, then, some things can be known with certitude, some things can be seen to be probable, and some things must remain forever a matter of doubt ; and since the human reason is liable to error, the need has been felt for some criterion or criteria by which we may know that we really know, and by which genuine certitude concerning the truth may be distinguished from the spurious certitude of delusion.

The proper test of truth is evidence, whether the evidence of a truth in itself or by participation in the evidence of some other truth from which it is proved. Many truths, indeed, have to be accepted on authority; but then it has to be made evident that such authority is legitimate, is capable of knowing the truth, and is qualified to teach in the particular department in which it is accepted. Many truths which are at first accepted on authority may afterwards be made evident to the reason of the disciple. Such in fact is the ordinary way in which learning and science are acquired. The error of Bonald's system of Traditionalism (which was condemned by the Church ) consists in its exaggeration, in its maintaining that the truths of natural religion are known solely on authority, that each generation simply inherits them from the preceding, and that unless they had been revealed to the first parents of the race human reason never could have discovered them.

If we take the cognitive faculties , one by one, the senses are not in themselves deceived concerning their proportionate object, but owing to circumstances they are so liable to deception that they need the vigilant supervision of the reason. The nature of sensible phenomena is not their object, but that of the reason. It should be remembered, however, that the scientific theories concerning the nature of sound, of colour and light, and of heat, have been thought out by the aid of data furnished by the senses, and therefore confirm the trustworthiness of the senses within certain limits. That men of science have no doubt as to the reality of extension, figure, movement, and space, any more than of force, is shown by their discussions concerning atoms, electrons, and ions. Consciousness is infallible as to the fact of its present states, e.g. that I am feeling warm, or well, or that I am thinking. The memory often errs, but often is trusted with certitude. Reason within a narrow sphere, is infallible, viz. in the perception of self-evident truth, e.g. that whatever is is, that every movement or change must have a cause, that things equal to the same are equal to each other. Truths which are clearly and easily deducible from self-evident truth share in their certitude. Next to such certitude, we may place the certainty of truths affirmed by the whole human race, especially as regards practical principles. "That which seems to all men, this we say is; and he who rejects this ground of belief will not easily assign a more solid one" (Aristotle, Ethics, X, ii). Universal consent is not, however, the sole criterion. To make it such was the error of Lamennais. Besides the truths resting on self-evidence (or easy deduction from it) and those resting on the authority of the human race, there is a considerable body of truth which each man of average intelligence comes to know with certitude in the course of his life. Most of these truths are first learned upon authority and afterwards verified by one's own reflection or experience. It may even be said that a practical Christian in the course of his life has by experiential verification an additional moral certitude of the truth of revelation, since he has experience of the power of the Christian religion to sustain the soul against temptation and to strengthen every virtuous and noble aspiration.


The Church pronounces judgment concerning the sphere of certitude, not so much for the sake of speculative knowledge, as in the interest of religion and morality. The mind of the Church upon this subject is manifested

(1) by placing books dealing with the question upon the Index, or by obliging ecclesiastics, or teachers in Catholic institutions, or editors of Catholic periodicals to subscribe some proposition;

(2) by "condemning" a proposition extracted from some work, in the sense in which it is found in that work;

(3) dogmatically, by a solemn affirmation of some truth or the anathematization of a falsehood. When a proposition is "condemned" or anathematized, the contradictory (not the contrary) proposition is asserted as true.

Concerning the sphere of certitude in religion, "Holy Mother Church holds and teaches that God, the first cause (principium) and last end of all things, may be known with certainty, by the natural light of the human reason, through the medium of things created " ( Vatican Council, Constitut. de Fide Cath., cap. ii); and this affirmation is supported by an anathema of the contradictory proposition (ibid., can. I). The condemnation of the Agnostic position concerning God may be studied in the Encyclical "Pascendi gregis dominici", in which the subject is admirably treated.

That "the freedom of the human will and the spirituality of the soul may be known with certainty, by the natural light of the reason ", is a truth which the pope, approving of a decree of the Sacred Congregation of the Index, obliged Bonnetty, editor of the "Annales de philosophie chrétienne", in 1855, to subscribe ( Denzinger, "Enchiridion", n. 1506). It would seem that these truths concerning the human soul are also in some measure implied in the definition and anathema cited above, concerning our knowledge of God ; for the attributes of God are known by the natural reason only, through the things that are made; and therefore freedom and morality must be known to be attributes of some creature before they can be attributed to God.

The limitation of natural knowledge and certitude has been repeatedly asserted by the process of placing books upon the Index, by the "condemnation" of propositions, by papal Briefs, and finally by a dogmatic decree, which alone is sufficient, viz: that of the Vatican Council (De Fide, cap. iv) which declares that

there are two orders of knowledge, distinct both in their source and their object; distinct in their source, for the truths of one order are known by naturalreason, and those of the other by faith in divinerevelation ; and distinct in their object, because, over and above the truths naturally attainable, there are proposed to our belief mysteries hidden in God, which can be known through divine revelation alone.

This solemn affirmation is supported by an anathema against any one who shall deny that there is an order of knowledge higher than the natural, or who shall say that man can naturally by progress attain at length to the knowledge of all truth (De Revelat., can. iii). Moreover, even as regards the natural knowledge of God, the Vatican Council teaches that

truths not unattainable by the natural light of thehuman reason have, by divine mercy, been revealed in order that they may be known by all easily, and with certainty and without any admixture of error (De Fide, cap. ii).

As regards certitude concerning the fact of Divine revelation, the Vatican Council teaches that the proofs are not, indeed, such as to make assent intellectually necessary (De Fide, cap. iii and can. v), but that they are sufficient to make the belief "agreeable to reason " (rationi consentaneum), being "most certain and accommodated to the intelligence of all" (De Fide, cap. iii). Anathema is pronounced against any one who shall say that Divine revelation cannot be made credible by "external signs" but only by "inner experience or personal inspiration" (De Fide, can. iii), and against any one who shall say that " miracles are not possible", or that " miracles can never in any case be certainly known" to be such, or that "by miracles the divine origin of the Christian religion cannot be properly proved " ( rite probari ; De Fide, can. iv). It is, then, moral certitude that is attainable by the reason as to the fact of Divine revelation. The certitude of faith is supernatural, being due to Divine grace, and is superior not merely to moral certitude, but to the certitude of physical science, and to that of the demonstrative sciences. When it is a question whether any particular truth is contained within the deposit of revelation, the certainty of faith can be obtained only from the authority of the "teaching Church ", but a human certitude may be obtained by arguments drawn from the inferior and subordinate authorities such as the Fathers and the "Schola Theologica".

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