“But can I really be certain?” – Moral Certainty, by Msgr P.J. Glenn, 1933

“An educated man looks for precision in each thing just so far as the the subject admits.”

Photo by Simeon Jacobson on Unsplash

This chapter, transcribed by The Bellarmine Forums and republished here with permission, considers the differing degrees of certitude.

Certitude admits of degrees in terms of the motives upon which it rests: but the three degrees are all types of true certitude, and each excludes the fear of error.

In the words of Aristotle:

“It is the mark of an educated man to look for precision in each class of things just so far as the nature of the subject admits; it is evidently equally foolish to accept probable reasoning from a mathematician and to demand from a rhetorician scientific proofs.”

In other words: when we are considering the many questions which trouble us today – such as whether someone is a member of the Church or not, or whether someone holds or has lost office, and whether we should avoid the Novus Ordo Mass, and so on – it would be foolish to expect a sort of scientific or metaphysical proof, as if metaphysical certitude is the only kind of true and sufficient certitude.

Those who think that they need this kind of certainty are left in a kind of limbo, perhaps trapped by indecision, or tortured with the same feeling as Macbeth, when he said:

“O, full of scorpions is my mind, dear wife!”

What is required, by contrast, is good judgment. Aristotle continues:

“Now each man judges well the things he knows, and of these he is a good judge. And so the man who has been educated in a subject is a good judge of that subject, and the man who has received an all-round education is a good judge in general.”

Before one can be a good judge of an answer, one must naturally be a good judge of questions. We do not have good judgement if we expect metaphysical certainty, or some impossible insight into another person’s mind, for questions which only require moral certainty in their answers.

This concept of moral certainty has many practical uses for our day. Declarations of authority are helpful and can, for example, create a universal obligation to assent to a particular proposition; and there may be several topics about which we cannot attain certainty without such a declaration. However, there are many topics about which we are capable of attaining moral certainty for ourselves; and it is not a virtue to close our eyes and deny this.

It is good to be humble, and keep an awareness of which questions we cannot answer with certainty (either in themselves, or because of something in ourselves). However, it is not “epistemically humble” to treat questions in this way if we can form morally certain judgments about them. Humility is rooted in reality and the truth – and shrinking from a proved conclusion may in some cases be pusillanimity, rather than humility.

This, of course, does not apply when a person is just not convinced of the arguments or evidence. However, when it comes to things like the validity of the sacraments, or whether a given person is a heretic and should be avoided, what we need is moral certainty. We should not ask for more than this – and when we attain it, we should be satisfied and embrace it.

So what is moral certainty? Let’s see how Msgr Glenn explains this topic, which is so vital for forming good judgments in our day.

This book from which this text is taken is currently quite hard to find online – it is available from Amazon US, and it is supposed to be republished in a fine edition soon. As Amazon Associates, we earn from qualifying purchases through our Amazon links. Click here for The WM Review Reading List (with direct links for US and UK readers).

Subscribe to stay in touch:


Mgr. Paul J. Glenn

This chapter studies the meaning of the term certitudeclassifies certitude, and discusses its degrees. The chapter is divided into two articles, as follows:

Article 1. Definition and Classification of Certitude
Article 2. Degrees of Certitude


  1. Meaning of Certitude                                                 
  2. Kinds of Certitude


Certitude may be defined as the firm and unwavering assent of the mind to known truth.

On the part of the subject, certitude requires a firm and unwavering assent, a steadfast adherence of mind to object. On the part of the object, certitude requires that this be truth and known as such.

In itself or formally, certitude is a state of mind. It is the condition of the subject. But it is not something which the subject produces within itself. It is a state of the subject which results from the manifestation of truth; the subject is made certain because truth is manifested to it. Now, the manifestation of truth is, in ultimate analysis, due to evidence, which is “the visibility of objective truth manifesting itself to the mind.” Hence, evidence is not only the criterion of truth; it is also the motive of certitude; it moves the mind to an unwavering assent to truth.

Formally subjective, certitude is causally objective. It is the objective truth, the evidenced truth, which begets the state of mind called certitude.

Certitude, as it exists in the subject, is a firm and unwavering assent and adherence of the mind to known truth. Its firmness excludes all hesitancy, all fear that perhaps, after all, the mind may be assenting to what is not true. Thus certitude differs from doubt and suspicion, in which there is no definite assent of mind, and from opinion, which is, at best, a hesitant or tentative assent involving fear that the opposite of what is assented to may be true. Certitude rigorously excludes all fear of error.

The firmness of the certain judgment, the certain assent, is due to a reasoned grasp of the motive of certitude. It, therefore, involves some measure of reflection on the part of the mind, some weighing and evaluating of motive. The so-called “spontaneous certitudes” are not full and perfect certitudes until the mind adverts to the weight of motive, of evidence, which calls for its firm assent. Of course, this does not mean that a true certitude requires of the mind a definite process of point-by-point checking according to a precise schedule of counts; it means that the mind not only gives firm and full assent, but, in some measure, realizes that it is right and reasonable to give such assent, before it is constituted in the state of perfect certitude.

As we have remarked in an earlier paragraph, it is usual to speak of “false certitudes,” that is, of the state of the mind as certain when it firmly assents to what is not true. Such a false certitude is indicated in the statement, “I was certain I was right, but I discovered that I was in error.” Now, in spite of this usage, in spite of this custom of speaking of false certitudes, we reaffirm our definition of certitude as the unwavering assent and adherence of the mind to known truth. The interest of Criteriology does not centre on the existence or possibility of false certitudes, but of true certitudes. Criteriology is interested in discovering and proving that the mind can know truth with certainty.

Sometimes we find certitude defined as the state of the mind which adheres firmly to one part of a contradiction without fear that the other part is really true. This definition is quite satisfactory if we understand that the part adhered to is known truth. The terms of the definition, however, call for a word of explanation. By a contradiction is meant the opposition of two judgments which stand flatly and accurately opposed. By one part of the contradiction is meant one of the two contradictory judgments. Two contradictory judgments exhaust the possibilities; they leave no ground between them. Between “it is” and “it is not” there is no neutral ground; it is one or the other; the possibilities are exhausted; and these are contradictories. Now, any relation which a judgment may express is capable of being considered in contradictory aspects, in two and only two contradictory aspects, for these two exhaust the possibilities; hence, one of the two must be true, the other false. Between the two judgments, “It is black” and “It is not black,” there exists perfect contradiction; one of the judgments must be true, the other must be false. There is nothing actual, nothing possible, in the realm of things of which color may be predicated, that is, neither “black” nor “not black.” Thus the two contradictory judgments “exhaust the possibilities.” The two contradictory judgments constitute a contradiction of which each judgment is a part. This explains the definition of certitude just given. The student is warned, however, to hold fast to his accurate knowledge of contradiction, and not to allow it to become confused with contrariety. Contrary judgments are opposed, and flatly opposed, but they are not accurately opposed; they do not exhaust the possibilities; they leave a middle or neutral ground between them. Thus the judgments, “It is black” and “It is white,” are opposed, but there is a wide ground of possibilities between them; many things of which color is predicable are neither black nor white, but red, or green, or yellow, or blue, and so on. The judgments, “It is white” and “It is black,” are contrary judgments, not contradictory judgments.

To sum up: Certitude is the unwavering assent and firm adherence of the mind to known truth. It is the adherence of the mind to the true part of a contradiction, without fear that the other (false) part is really true. The mind which unwaveringly adheres to what appears to be true, but is really false, is constituted in the state of error, and not of true certitude.


1. Subjective and Objective Certitude.

Certitude is properly a state of mind with reference to truth; it belongs to the thinking subject. Hence, certitude is formally subjective. Yet causally it is objective, and hence the term certitude is sometimes transferred to the objective truth to which the mind assents. Therefore, the term subjective certitude means the unwavering assent of the mind to known truth; objective certitude is the truth to which the mind assents. The statement, “I am certain that God exists,” indicates subjective certitude. The statement, “The existence of God is a certainty,” indicates objective certitude.

2. Metaphysical, Physical, and Moral Certitude.

Metaphysical certitude is the unwavering assent of the mind to what things in their essence and nature must be. Our certitude that man is an animal, or that a totality is greater than any one of its component parts, is metaphysical, for the very concept of man’s essence, the very ideas of totality and part, make the judgments inevitable. Metaphysical certitude is also called absolute certitude.

Physical certitude is the unwavering assent of the mind to what expresses the order of nature and the consistency of natural laws. Our certitude that a dead man will not return to earthly life is physical; so also is our certitude that snow must be white, and that good seed will sprout when planted under favorable conditions in fertile ground.

Moral certitude is the unwavering assent of the mind to what expresses the normal mode of human conduct. Thus we have moral certitude that a mother will love her child. It is to be noted in passing that the expressions, “It is morally certain,” and “It is a moral certainty” are “newspaper English” for a greater or lesser degree of “probability.” These expressions, as used casually in unscientific speech, are not to be confused with the terms moral certitude and morally certain, used in Criteriology. For these terms do not indicate a mere opinion, however probable, but true certitude, a full and unwavering assent of the mind upon evidence taken from the normal human mode of action, evidence which the mind finds sufficient to win its full assent.

That which is metaphysically certain cannot be otherwise, cannot even be conceived of as existing otherwise. That which is physically certain can be conceived of as existing otherwise, but not unless the order of nature be suspended by virtue of a higher law. Thus physical certitude is certitude of that which must be, unless a miracle intervenes. That which is morally certain can be conceived of as existing otherwise, and may in fact exist otherwise without the intervention of a miracle, but not without the intervention of a human will which acts in a manner contrary to the normal and rational mode of human conduct, that is, of such conduct as proceeds from the deliberate will of a normal person. The basis and evidence of metaphysical certitude is the very essence of things; that of physical certitude is the constancy of nature; that of moral certitude is the constancy or normal human conduct.

I am metaphysically certain that a circle cannot be square. I am physically certain that bodies at rest tend to remain at rest. I am morally certain that a man of virtue will not suddenly become vile.

Another phase of moral certitude is that which the mind achieves by adverting to the evidence of normal human conduct in the circumstances. If I am in doubt whether a bill is paid; if I can find no evidence in writing that it was or was not paid; then I consider the character of the debtor, and the character of the creditor. I find that the debtor is scrupulously honest. I find that the creditor is exact in keeping accounts. By the evidence of these facts, by the evidence of what an honest debtor and a business-like creditor would normally do in the circumstances, I can arrive at moral certainty that the bill was paid. But if I an unable to determine the issue by such investigation; if the character of the debtor and the creditor leave me in doubt about the bill, then I fall back upon a reflex principle, viz., “A law of doubtful application cannot bind to certain obligation.” This principle expresses the normal, sane view of prudent men; it is a dictum of common human sense. Hence, direct methods failing, I may resolve my doubt by invoking this reflex principle and may achieve moral certitude thereby.

Subscribe to stay in touch:

3. Certitude of Science and Certitude of Faith.

The certitude of science is the unwavering assent of mind to a truth that is understood in itself, a truth that is known because it is self-evident (immediate scientific certitude) or because it has been clearly reasoned out (mediate scientific certitude). The certitude of faith is the unwavering assent of the mind to a truth known on authority. If the witness, the authoritative propounder of the truth to be believed, is God Himself, then our certitude is that of divine faith. If the witness be a man, or men, the certitude is that of human faith.

Certitude of faith is not a blind or unreasoning certitude; indeed, certitude is by definition a reasonable assent of the mind to known truth. The truth to which the assent of faith is given is known indirectly, that is, it is known in the recognized validity of the testimony which evidences it, but the point is that it is known.

The certitude of science and that of faith will be discussed in detail in a later chapter.

4· Natural and Supernatural Certitude.

Natural certitude is the unwavering assent of mind to truth manifested (scientifically or by human authority) unaided human reason. Supernatural certitude is the firm assent to truth manifested under the light of Revelation to a mind fortified by divine grace.

5. Common and Philosophical Certitude

Common or vulgar certitude is the certitude of daily experience, the certitude into which we make no scientific investigation. By common certitude we are sure of our surroundings, of our own feelings, of our likes and dislikes, of our actions and employments. By common certitude a man knows that he is hungry or thirsty, that he feels well or ill, that he is called by name, that he is successful or unsuccessful in business, that he must go to work or that he may take a holiday, and so on. In many matters this vulgar or common certitude is true certitude or can become full-fledged certitude by a little reflection. For common certitude is our state of mind with regard to many self-evident truths that bear upon the rational conduct of life, individual and social, physical, mental, and moral. In these matters the spontaneous movement of nature which leads to the assent of common certitude cannot be deceiving or nature herself is deceiving; and if nature be deceiving, there can be no trusting of natural powers, and no achieving of science or certitude at all.

Philosophical certitude is that which comes of the mind’s explicit investigation and grasp of the ultimate reasons and motives for its unwavering assent.


In this article we have defined certitude and have studied the definition in detail. We have listed certain kinds or varieties of certitude, explaining each in turn. All these varieties are aptly grouped into two classes, two kinds of certitude, viz., certitude of direct evidence, and certitude of indirect evidence, that is, certitude of faith.


  • Meaning of Degrees of Certitude
  • Actual Degrees of Certitude


A “degree” or “grade” suggests a step in a series, like a rung in a ladder or a stage in a stairway. If there are degrees of certitude, this must mean that some things are more certain, some things less certain, some things most certain.

Certitude has two points about it that may be considered when we ask whether there are or can be degrees of certitude. One of these is the fact that certitude is a firm assent of the mind excluding fear of the contradictory. The other point is that certitude rests upon motive, upon evidence, and this may be investigated to see whether it admits of degrees. Considering the first point, viz., the exclusion of fear of being wrong, we find no degrees of certitude. For every certitude, to be certitude at all, must perfectly exclude all fear of error. This is part and parcel of the very definition of certitude. Considering the second point, viz., the motives of certitude, we discern degrees, and we shall study them in the next paragraph.


The assent of the mind to known truth may be regarded as subject to grades or degrees according to the character of the motives upon which the mind relies in giving its firm assent.

Thus metaphysical certitude, founded as it is upon the very essences of things, is wholly absolute, it knows no “ifs” or “provided that’s.” 

Physical certitude rests on the regularity of nature, and depends upon the uninterrupted and unthwarted continuance of natural processes. It rests upon the condition, “provided that nature is not interfered with; provided there is no miracle.” Hence metaphysical certitude is a higher grade or degree of certitude than physical certitude inasmuch as the absolute or unconditioned is a higher grade than the conditioned. To illustrate: my certitude that a circle is “perfectly round” is metaphysical certitude, for perfect roundness is the very essence of the circle.

Thus I know that a “square circle” is impossible, that it simply cannot be, even by a miracle. My certitude that the dead and buried Lazarus will not walk again among men in earthly existence is physical certitude; it rests upon the constancy and consistency of nature and upon the condition that no miracle intervene to make an exception to that consistency. But a miracle does intervene; the condition is not fulfilled; Lazarus comes back to life. Thus physical certitude is a lesser grade of certitude than metaphysical certitude.

Again: moral certitude, while true certitude, depends upon the rational and normal conduct of men. I am certain that a mother loves her child, even though a rare exception to this rule may occur without the intervention of a miracle. Hence moral certitude rests upon a condition that is more likely to have an exception than the condition upon which physical certitude rests; in so far, moral certitude is a lesser degree of certitude than physical certitude.

Metaphysical, physical, and moral certitude are therefore, not only classes of certitude; they are grades or degrees of certitude. They are degrees or certitude because they rest upon motives of graded necessity for their acceptance by the mind.

In a word, there are degrees of certitude founded upon the motives which impel the mind to give its unwavering assent. But there are no degrees of certitude in the sense of degrees in the exclusion of the fear of error which characterizes the unwavering assent. If the smallest fear of error should creep in, the assent of mind would no longer be certitude, but opinion.


In this very short article we have studied the interesting and important matter of degrees of certitude. We have seen that certitude admits no degrees in its exclusion of the fear of error, but does admit degrees with respect to the motives upon which it rests. The degrees of certitude in the descending scale are metaphysical, physical, and moral certitude.

This book is currently quite hard to find online – it is available from Amazon US, and it is supposed to be republished in a fine edition soon. As Amazon Associates, we earn from qualifying purchases through our Amazon links. Click here for The WM Review Reading List (with direct links for US and UK readers).

From: Right Rev. Msgr. Paul J. Glenn PH.D., S.T.D., CRITERIOLOGY — A Class Manual in Major Logic, B. Herder Book Co., St. Louis & London, 1933. Book 3, Ch. 1, pp. 141-153

Transcribed and published by the Bellarmine Forums. Reprinted with permission.


As we expand The WM Review we would like to keep providing our articles free for everyone. If you have benefitted from our content please do consider supporting us financially.

A small monthly donation, or a one-time donation, helps ensure we can keep writing and sharing at no cost to readers. Thank you!

Monthly Gifts

Subscribe to stay in touch:

Follow us on Twitter, Telegram, Facebook and Gab.

Don’t forget!

See here for The WM Review Reading List in full.

Leave a Reply