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The term certitude derives from the Latin, cernere (Gr. ερίανειν), which means to resolve, decide after seeing the evidence. St. Thomas Aquinas defines certitude as "the firmness of the adherence of a knowing power to the thing known" (In 3 sent. 26.2.4). Primarily a quality of the judgment, certitude can be considered positively to indicate the firmness of the mind in its assent and negatively, the exclusion of all prudent fear of error. It is distinguished from other states of mind such as doubt, which is an inability either to affirm or deny; and opinion, which is the acceptance of a judgment as probable. Since the intellect is made for knowing truth, and its perfect actuation is had only when the truth is known with evidence, formal certitude is had when what is known presents itself as objectively evident.

Historical Development

Among the early Greek philosophers the question of certitude was not formally considered, although the reasonings of the early cosmologists implied the view that ordinary certitudes were not reliable. With the rise of the sophists there developed an explicit questioning of the ability of the human mind to arrive at true and certain knowledge. For some, such as heraclitus, Protagoras and Gorgias, reality was in such flux that it could never be known as it is.


Against these, socrates and plato contended the possibility of the human mind's arriving at true certitudes. While Plato fostered a skepticism relative to sense perception, he claimed certitude to be attainable in the intelligible sphere, where knowledge is had of Ideas or Ideal Forms. These are the ultimate realities and the only objects of knowledge in the strict sense. For aristotle first principles are self-evidently certain and hence indemonstrable. He held that sensible beings can be known by virtue of the form (the inner principle of determination) and that all the materials of intellectual knowledge are somehow derived from and through the senses.

After Aristotle, speculative philosophy made little progress. For the Epicureans the one thing necessary was pleasure, in the sense of a lack of perturbation ('αταραξíα); and truth, virtue and all else are of value only insofar as they promote this. The Stoics implied that (subjective) certitude is attainable, especially in the knowledge of what constitutes an ethically good and wise life. Against the alleged certitude of this position the Skeptics reacted and for about five hundred years (c. 300 b.c.a.d. 200) skepticism exercised great influence in Greek and Roman thought.

St. Augustine's Contra academicos is a refutation of the skeptical positions of the New Academy; and in general the Church Fathers and the scholastics through the Middle Ages discouraged skepticism and affirmed the ability of the mind to know with certitude. They distinguished between what the mind knows by the natural light of reason and what it accepts on testimony and between intrinsic and extrinsic evidence; the latter being important for Divine Revelation (confer St. Augustine, C. acad. 2.7; St. Thomas, In 3 sent. 26.2.4; ST 2a2ae, 2.1.) In the nominalism of william of ockham, however, skepticism did find some expression.


From its beginning, modern philosophy was characterized by the firm conviction that if the true object of the mind is philosophically determined, or if its proper limits are faithfully respected, man is capable of certitude. One may be asked to admit that the object of reliable knowledge is the unique divine substance (spinoza), or the Absolute Spirit in itself and in its self-manifestations (hegel); true knowledge may be limited to ideas and their interrelation (British empiricism), or to sense presentations as informed by the categories of the understanding (kant); but with these qualifications settled, the outstanding thinkers are convinced that truth and certitude are attainable.

Thus, descartes, facing the anti-intellectualism of the Renaissance and the atheism and skepticism of his day, sought to find a new and firm foundation for certitude in metaphysics. Beginning with the self and using the technique of doubt, he was convinced that his reflections finally overcame doubt, gave him true knowledge of his own existence, of God and of the external world. rationalism glorified the power of the mind to know and to build systems, but it has been accused of vastly exaggerating man's capacity for certain knowledge. While the empiricists limited the immediate objects of human knowledge to ideas or impressions, they (apart from David hume) were convinced that in this narrow area certitude was to be had. Kant, impressed by the success of the physical sciences, decided that only scientific truth and certitude were reliable; hence metaphysics, which deals with "questions such as cannot be answered by any empirical employment of reason, or by principles thence derived," is not available with the certitude of evidence (Critique of Pure Reason, Introd. A3; B6). So questions on the nature of the soul, of the world and of God lead only to illusion.


As a result of the works of modern philosophies, scholastic philosophers have devoted much time to questions of truth and certitude. In the 19th century many of them, influenced by the thought of J. balmes, held that man naturally possesses some absolutely certain truths that need no justification whatsoever. Later, Cardinal Désiré mercier and others taught that man's many spontaneous certitudes need further philosophical reflection in order to establish the human capacity for truth and to arrive at reflex certitudes. Others admit some naturally known certitudes, and since these are known implicitly in each judgment, one needs merely to become explicitly aware of them.

Leaving scholasticism aside, one can say that the contemporary philosophical scene is very complex, but that one of its outstanding features is an antimetaphysical attitude that becomes an outright skepticism for many. This is due in no small measure to the skepticism of Hume, who paved the way for most of contemporary empirical philosophy and for the antimetaphysical views of positivism, phenomenalism and pragmatism. Developments in scientific method and studies in the nature of language and logic have contributed much to the skeptical mood of logical positivism and linguistic analysis. When there is admission of truth, it is often with a relativistic twist, in terms of scientific verification, utility (personal or public) or adaptation to an evolving environment.

Kinds Of Certitude

That there may be intellectual convictions or firm assents of the mind of various kinds, can be seen by brief reflection. One may be certain that Julius Caesar was stabbed to death; that the human soul is immortal; that another person loves him; that God exists; and that he himself exists. In all these areas certitude may be claimed and yet it is obvious how different are the assents, for example, to one's own existence and to Caesar's murder. Moreover, whether because of prejudice or training, men do at times assent to a false doctrine or position with a dedication worthy only of the truth. Hence it has become usual and necessary to distinguish various kinds of certitude.


Since certitude is primarily a characteristic of human assent, it can be said that all certitude is subjective. However, it is called purely subjective when evidence is lacking, or is not known to be present, for the firm assent then given is in reality only an affective disposition of the subject, who believes without doubt and without proper motivation that he possesses the truth. Objective certitude means a firm assent of the mind to a known truth, an assent motivated by the evidence, and wherein the known motive for assent excludes all prudent fear of error.


This division, common in scholastic manuals, is made in view of the foundation on which the certitude rests. The former is said to rest on the natures or essences of things; the latter on the connection between finite natures and their operations. Absolute (or metaphysical) certitude is had in the knowledge of self-evident truths, such as the proposition that a thing cannot simultaneously be and not be; of demonstrated conclusions, such as the spirituality of the soul; or even of the contingent fact of one's own existence. When any given truth is known with metaphysical certitude, this means that the denial of that truth would be a denial of the very nature of what is known; hence its opposite is excluded as utterly impossible. However, in the operations of finite beings, it is possible that the nature, while remaining essentially unchanged, may be impeded in the production of its natural operation or effect, and thereby a note of the conditional or hypothetical enters in. Since finite agents are divided into the two classes of (1) freeman in his deliberate actsand (2) determinedall other material beings and even man in his nonfree operations such as growth conditional certitude is of two kinds, physical and moral.


This certitude characterizes assent to concrete applications of physical laws. Such laws come to be known through induction and they tell how nonfree natures operate. Presupposing the accuracy of observation and the correct use of induction, such laws are themselves metaphysically certain, since they reveal the natures of things. In simple examples, it is of the nature of fire to burn, of unsupported heavy bodies to fall, of hydrogen and oxygen to unite to form water. However, when it comes to the operation of these laws in concrete instances, some defect of matter or agent may impede such operation from taking place. The law is still certain conditionally, however, on condition that such defects do not occur.

Scholastic manuals usually insist here that divine cooperation is also necessary and that God can (for some special reason) suspend a physical effect without at all changing the nature of the agent (see miracles). Hence, although absolute certitude is not to be had, one can and does give a firm assent without prudent fear of error in given instances. One can be certain that food will nourish him and that fire will burn a dry log. This assent is motivated by the knowledge of how the given nature operates and granting no indication of divine intervention, it provides a certitude that is called physical.


This is said to be had in some concrete applications of moral laws. The laws are arrived at by induction and they enunciate truths about how human beings freely operate. Traditional examples have to do with maternal love, the natural veracity of men and the reliability of historical testimony. Since exceptions to such "laws" can be had by the abuse of free will, it is clear that the necessity found in this area is far less rigorous than in the working of the laws of nature; so certitude here is not easily had and when had, is of a very different kind. However, presupposing knowledge of the apposite law of human conduct and knowing from the circumstances that there need be no fear of an exception, one can have moral certitude about his friend's loyalty, his wife's fidelity or a particular person's veracity.

Some philosophers have been willing to call only metaphysical certitude true certitude; and they speak of physical and especially of moral certitude as only very high probabilities. However, for others this places too stringent limitations on the nature of certitude and fails to recognize that scientific progress presupposes physical certitude and that human life and communication presuppose the reliability of moral certitude.


Certitude is divided also into speculative and practical. The former is taken to refer either to what is theoretically valid or to the sphere of being in general. The latter means either a high degree of probability that is sufficient for the ordinary activity of daily living, or refers to particular judgments applying law to a specific case, to what actually ought to be done (see prudence).


Considering the role of the will in assents, one can speak of necessary and free certitude. The former is had in response to truths so immediately evident that the intellect, having once adverted to them, cannot refuse its assent. Here the will merely directs attention to the proper consideration. Examples are: one's own existence, one's immediate experience, the principle of contradiction. However, most truths are not so immediately evident and the will usually has a more important role in the exercise of judgments. Truths such as the existence of God, of the spirituality of the soul and those deriving from human testimony may indeed be assented to firmly and securely; but they can be, and have been, doubted, and they do not force the mind's assent. These are free certitudes.


Natural certitude is sometimes taken to mean the spontaneous, pre- reflective convictions of men relative to such truths as one's own existence, the existence of other beings or the need of living a morally good life; in this sense it is distinguished from reflex certitude, which is known to be based on objective evidence and which presupposes awareness of the powers and limits of the human mind. However, from the point of view of the means whereby truth is acquired, natural certitude refers to truths that are legitimately acquired by the natural powers of the human mind in the light of objective evidence; and is thus distinguished from supernatural certitude, which is had in truths that are accepted on the authority of God's revealing.

Objective Natural Certitude

Of special importance for philosophy are firm assents that are acquired by the natural operations of the human mind (hence not in virtue of revelation) and are based on the self-manifestation of what is known. Whenever this sort of certitude is had, no matter what the process through which the being that is known manifests itself in one or other intelligible aspect, it is always characterized by the note of necessity. In this sense what is assented to with this sort of certitude must present itself as infallibly and necessarily true. Only in this way can the intellect be perfectly actuated in its natural drive for truth and find that satisfaction and joy that results only from the secure possession of its proper good, which is the truth.


This sort of certitude can be had by the intellect in either its immediate or mediate assents. In the knowledge of first principles one is dealing with truths that can be recognized and affirmed by a sort of natural instinct or intuition, once the meaning of the subject and predicate has been grasped. Thus, if a person knows the meaning of "whole" and of "part," he can immediately affirm the relation between them. As St. Thomas says, first principles "are not acquired by reasoning, but from the sole fact that their terms are known" (In 4 meta. 6.599). This holds for such truths as the principles of contradiction, of identity, of finality, etc. In these cases there is a recognition of truths that are infallibly, necessarily and evidently true; whose evidence, in fact, is self-manifesting; and whose truth is so totally and so evidently present that there can be no room for doubt, hesitation or any sort of incertitude.

While these principles are grasped with supreme evidence and certitude, it must be admitted that they are vague in content and come far from satisfying man's desire for truth. St. Thomas looks on them as a sort of seedbed (De ver. 18.4.) wherein truths are contained in an imperfect manner and must be brought to flower in the actual and certain knowledge of what is virtually contained in the principles. By this is meant the vast area of mediately known truths that are acquired by demonstration.


Demonstrated truths are all conclusions of science and philosophy derived from premises that are certain and evident, so that the new truths themselves are, by the process of demonstration and through the mediating function of some middle term between subject and predicate, rendered evident and certain. Unlike the evidence and certitude of first principles, the evidence and certitude of conclusions are themselves mediate and derived. Yet, even in these truths, it is the object known, that thus mediately manifests itself to the mind and specifies the intellectual act. It does reveal itself as necessarily and infallibly true and it can be justified in the light of first principles; hence this sort of scientific certitude also results in the perfect satisfaction of the mind in its quest for truth.

As St. Thomas points out, the certainty of the conclusions rests ultimately on the evidence and certitude of first principles; hence the function of demonstration is to render the evidence of the conclusion present to the intellect by showing its connection with first principles. "The whole certainty of scientific knowledge arises from the certainty of principles. For conclusions are known with certainty when they are reduced to principles. Therefore, that something is known with certainty is due to the light of reason divinely implanted within us " (De ver. 11.1 ad 13).

Church Teaching On Certitude

In this matter the Catholic Church has consistently and officially taken a clear stand. Its expressed views are:(1) The human mind is capable of arriving at truth. (2) Of itself it is incapable of arriving at knowledge of supernatural truths concerning God and man. (3) Even with regard to some truths about God that can be naturally known, it is not easy for man to arrive at them and so it is fitting that God should come to man's aid by revealing them to him.


While these themes can be illustrated from the whole history of Church teachings, a few brief references to the documents will suffice. On the ability of the human mind to know truth and to know it with certitude: "The reasoning process can prove with certitude the existence of God, the spirituality of the soul and the freedom of man" [H. Denzinger, Enchiridion symbolorum, ed. A. Schönmetzer (32d ed. Freiburg 1963) 2812; confer, 3004, 3026]. Pope Pius XII presents the abiding views of the Church in this matter when he says: "It is well known how highly the Church esteems human reason for its function to demonstrate with certainty the existence of God, personal and one; to prove beyond doubt from divine signs the foundations of the Christian faith itself; to express properly the law which the Creator has imprinted in the hearts of men; and finally to attain to some understanding, indeed a very fruitful one, of mysteries" (Enchiridion symbolorum, 3892). Speaking of scholastic philosophy he continues: "This philosophy, acknowledged and accepted by the Church, safeguards the genuine validity of human knowledge, the unshaken metaphysical principles of sufficient reason, causality and finality; in a word, the possibility of attaining certain and unchangeable truth" (ibid. ).


However, the Church has been fully aware also of the fact that what man can learn by his own natural powers is quite limited. These limitations are found in two areas, the natural and the supernatural. With an eye to constant Church teaching, Vatican Council I clearly points out that there is an order of knowledge entirely beyond the natural powers of man, a supernatural order, wherein revelation is required if man is to learn anything at all about it: The Church has always held and holds "that there are two orders of knowledge, distinct not only in origin but also in object. They are distinct in origin, because in one we know by means of natural reason; in the other, by means of divine faith. And they are distinct in object, because in addition to what natural reason can attain, we have proposed to us as objects of belief mysteries that are hidden in God and which, unless divinely revealed, can never be known" (Enchiridion symbolorum, 3015). This position is reinforced by a corresponding canon (Enchiridion symbolorum, 3041).


Even in those matters pertaining to God that the human mind can learn by the natural light of reason, the same Council explicitly states that such truths have also been revealed by God so that they may "easily be known by all men with solid certitude and with no trace of error" (Enchiridion symbolorum, 3005).

Relative to the acceptance of the fact of revelation, the Council teaches that God provides all the means necessary for (moral) certitude in this matter. To ensure the reasonableness of our assent, "God has willed that external proofs of His revelation, namely divine acts and especially miracles and prophecies, should be added to the internal aids given by the Holy Spirit" (Enchiridion symbolorum, 3009). This position is reaffirmed in the corresponding canons and the possibility of knowing miracles with certitude is restated in the words: "If anyone says that miracles can never be recognized with certainty let him be anathema" (Enchiridion symbolorum, 3034).

While the certitude respecting the fact of revelation is normally moral, the certitude had in the supernatural act of faith itself, made by divine grace and having the authority of God Himself as its motive, is of a higher quality than any natural certitude.

Certitude And Faith

Supernatural certitude, having as its motive not the evidence of what is assented to, but the authority of God revealing and being informed by grace, has special pertinence in the matter of the virtues of faith and hope. Revelation, by providing the believer with the opportunity for a secure assent to new truths, is a source of new certitudes and of renewed security in assents to some naturally knowable truths about God's existence and nature.

In the process of passing from unbelief to belief, we can distinguish various steps and indicate briefly the role of certitude in each. The initial steps, which help to turn the person towards the acceptance of faith, concern things that are naturally known and for which natural certitude can be had. As initial steps towards faith, these natural acts are motivated by divine grace. In the process one must come to know and admit the credibility of God as witness to truth; and as this rests on the demonstrated existence and veracity of God, it is known in an evident and certain judgment. There must then follow the knowledge that God has actually revealed some particular truth; and the acceptance of this, in order to be reasonable, must rest on such proofs as will render it evident and certain to the human mind. Finally, in making the act of faith itself, one assents firmly and with certainty, to what God has revealed, motivated only by the knowledge that He has so revealed. In this assent the mind does not see or understand what it believesthe object of faith, for example, the Holy Trinitybut it recognizes with certitude that it should assent for motives that are now evident. In making the full act of assent, the will has an important role to play, since the object is not evident and therefore cannot determine the intellect.

Certitude And Hope

The supernatural virtue of hope is a habit whereby man confidently expects eternal happiness as well as the means necessary to arrive at it. Thus the acts of this virtue have as their object the possession and enjoyment of God by vision and love, as well as the supernatural help to attain this end; they have as their motive God's fidelity, power and mercy. In addition to this divine side, there is the human side, man's cooperation with grace and his fidelity to the will of God. Insofar as hope rests on the firm foundation of God's fidelity to His promises, it is characterized by complete certitude, since God will most certainly fulfill His promises. However, insofar as hope includes the human element of man's cooperation with, and fidelity to, grace and his final perseveranceand of these one cannot be so sureit is always colored by some uncertainty. As St. Paul says, "work out your salvation with fear and trembling" (Phil 2.12) and this must be because we may fail and not because God can fail us. St. Thomas points out that "filial fear is not opposed to the virtue of hope, for thereby we do not fear that what we hope to obtain through God's help will fail us, but rather we fear that we may withdraw ourselves from that help" (ST 2a2ae, 19.9 ad 1). So hope, as an act of the will elicited under divine grace, does not have the same sort of certitude as an act of faith.

Rejection Of Certitude

Only a radical skepticism positively rejects all certitude and gives up in despair when faced with the problems of human knowledge. Still, very many schools of philosophy do, at least implicitly, reject the possibility of certitude in one area or another. Such schools have flourished not only in the ancient, but also in the modern world and are treated in detail elsewhere in the Encyclopedia (see kepticism; knowledge, theories of).

Summarily it can be said that in many contemporary philosophies there is either a skepticism about sense knowledge and a consequent rejection of the noetic role of sensation, or a skepticism about intellectual knowledge and a consequent limitation of valid knowledge to the empirically verifiable. Concretely what is needed is an analysis of both knowledge and certitude that recognizes the complexity of the knowledge process. In the attainment of knowledge one finds aspects of singularity and universality, of necessity and contingency, of materiality and spirituality and of identity and diversity between knower and known. These elements are not easily harmonized in any theoretical exposition of the nature of knowledge. However, an adequate explanation must preserve all the experienced elements, even those difficult to reconcile. Because knowledge is of the universal and necessary, one cannot reject the singular and the contingent. Knowledge means an identity between knower and known; still, the diversity between them cannot be denied.

Since man is a composite unity of body and soul, of mind and matter, his cognitional situation reflects this; he is limited neither to pure sense perception nor to a purely intellectual vision entirely divorced from the senses. The human contact with experienced being occurs at various levels. One has sense knowledge of sensible beings; one also has intellectual knowledge of these same beings according to one or another aspect of their intelligible structure. With these as a foundation, one can go on to a deeper intellectual knowledge of material things and their operations, of one's own mental and volitional activities as spiritual and finally of God.

The problem of human certitude is identical with the general problem of human knowledge, with the study of its proper object and of its nature. The doubt that characterizes skepticism is self-defeating, whether as a general theory or as limited to some area of inquiry and results in despair and the abandonment of inquiry rather than a fruitful investigation and evaluation of the facts.

See Also: epistemology; knowledge; truth.

Bibliography: thomas aquinas, Truth, tr. r. w. mulligan et al., 3 v. (Chicago 195254). r. f. o'neill, Theories of Knowledge (Englewood Cliffs, N.J. 1960). l. m. rÉgis, Epistemology, tr. i. c. byrne (New York 1959). i. trethowan, Certainty, Philosophical and Theological (Westminster, Md. 1948). w. a. wallace, The Role of Demonstration in Moral Theology (Washington 1962). Philosophy of Knowledge, eds. r. houde and j. mullaly (Philadelphia 1960). j. owens, An Elementary Christian Metaphysics (Milwaukee 1963). f. a. cunningham, "Certitudo in St. Thomas Aquinas, " The Modern Schoolman, 30 (195253) 297324. s. harent, Dictionnaire de théologie catholique, ed. a. vacant et al., 15 v. (Paris 190350) 6.1:201215. h. denzinger, Enchiridion symbolorum, ed. a. schÖnmetzer (32d ed. Freiburg 1963).

[r. f. o'neill]