Pope Francis has stated multiple times that Amoris Laetitia is rooted in the moral theology of Thomas Aquinas. The citations to Aquinas in Chapter eight have been commented on by others, but quotations from the works of Aquinas are not the only way in which Amoris Laetitia (AL) draws on the Angelic Doctor. More fundamental is the Thomistic foundation that is not directly alluded to in AL but which nevertheless grounds much of the controversial statements of chapter eight.  That foundation consists of  Aquinas’ answer to the question: “Can mortal sin become venial?”

Like many of his answers, his answer to the question “can mortal sin become venial?” is both yes and no. Logically, the only way for this to be possible is by making a distinction.

Aquinas makes a distinction between sins that are generically venial (or mortal) according to their object, and sins that are venial “from the cause”. What makes a sin venial “from the cause” is imperfection in the source of the action, “as when a sin contains something diminishing its guilt, e.g. a sin committed through weakness or ignorance: and this is called venial ‘from the cause’”(II-I Q.88 Article 2).

On the other hand, sins “can have a determinate genus, so that one sin may be venial generically, and another generically mortal, according as the genus or species of an act is determined by its object” (II-I Q.88 Article 2).

It is from this generic perspective that mortal sins cannot become venial sins.


“…a sin which is generically mortal, can become venial by reason of the imperfection of the act, because then it does not completely fulfill the conditions of a moral act, since it is not a deliberate, but a sudden act, as is evident from what we have said above (Article 2)” (II-I Q.88 Article 6).

Hence, “it may happen, on the part of the agent, that a sin generically mortal becomes venial, by reason of the act being imperfect, i.e. not deliberated by reason, which is the proper principle of an evil act” (II-I Q.88 Article 2).

So the answer to the question “can mortal sin become venial” is NO if we view sin generically, ‘by its object’. However, the answer is YES if we consider sin from the disposition of the agent, ‘by its cause’.

Now why is it that when the pope reminds us, like Aquinas before him, that mortal sin becomes venial in some messy situations, a great hand-wringing and hair pulling and gnashing of teeth goes on? “This is justifying objective sin”, the objection goes. “This is allowing exceptions to the objective moral law”, “this is a free pass for adultery”, “this destroys the very foundation of Catholic morality!” What explains this reaction?

Well, one thing that explains it is these two aspects of human action are being conflated. Because if you don’t recognize the category of the venial sin ‘by the cause’ and only recognize sins ‘by the object’, then of course every effort to posit a venial sin ‘by the cause’ is going to look like a denial of sin ‘by the object. Every attempt to draw attention to the fact that ‘adulterers’ may in fact be only sinning venially in some messy circumstances (and therefore possibly eligible for communion), is taken as a denial of adultery per se, or as a double standard, or situation ethics (the denial of objective sin). The practical consequence of not making this distinction is that all talk of mitigating circumstances will not compute. The message will just be interpreted as “No Objective sins” or more specifically, “Adultery is not a Mortal sin” or “adultery is not grave matter”.

But to say that the mortal sin of  “adultery” may become venial in a particular act because of ignorance or weakness is not to say that there no longer exists adulterous kinds of acts, or that a free pass for adultery exists for some people, but only that some particular acts cannot be characterized morally as adultery because of the imperfection of the act at its source. Unlike some critics who think that the consequences of this is the destruction of all of Catholic morality, Aquinas says that under such circumstances it is the “species” that is destroyed (the species of adultery in this case). It’s not destroyed generically, somebody somewhere will still be guilty of committing adultery, but the species is destroyed in this particular action by this particular person under these particular circumstances at this particular time.

Why is such a basic distinction, present in law and catechisms, now suddenly mystifying and suspicious? Why is elementary moral theology now being side-eyed and dismissed as loopholes?

I believe it’s because some Catholics are uncomfortable with the existence of weakness. They don’t believe that the weak exist because they don’t believe that weakness is really a thing (the Neo-Pelagian mentality?). That’s why everything comes back to ignorance for them, “Oh just inform the sinner of his mistake and all will be well. If he continues sinning, that’s on him.” But weakness is independent of ignorance. Weakness is not a knowledge problem. Nor is it a repentance problem. The person who is weak may know the law, agree with the law, love the law, and yet still can’t obey it. That’s what weakness means.

Hence, “more is involved here than mere ignorance of the rule. A subject may know full well the rule, yet have great difficulty in understanding ‘its inherent values’, or be in a concrete situation which does not allow him or her to act differently and decide other-wise without further sin” (AL 301).

Nevertheless, people continue to characterize unfree, morally compromised, or coerced actions as if they were free, consensual, and perfect acts of moral agency. Making these category errors between freedom and weakness, between sins ‘by the object’ and sins ‘by the cause’, it’s no wonder they see chapter eight as a threat to the whole foundation of moral theology.

So Pope Francis is echoing Aquinas when he says “it is reductive simply to consider whether or not an individual’s actions correspond to a general law or rule, because that is not enough to discern and ensure full fidelity to God in the concrete life of a human being.” (AL 304)

Because “moral acts derive their character of goodness and malice, not only from their objects, but also from some disposition of the agent” (II-I Q.88 Article 2). A ‘disposition’ like weakness or ignorance. The attempt to measure human beings merely by holding their actions up to an objective rule is what the philosopher Rocco Buttiglione calls “ethical objectivism” – the opposite error of the subjectivism of situation ethics.

Amoris Laetitia doesn’t repudiate the objective view of morality, but it does ask us to stop neglecting the subjective disposition of the agent, especially when we are judging a person’s fidelity to God.


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Husband, father of six, idea-tinkerer, graduate school drop-out. Having previously lived amongst the cacti and coyotes of Arizona, Brian now resides in the Canadian prairies.  Brian is a co-conspirator of Where Peter Is.

Thomas Aquinas: Ghostwriter of Amoris Laetitia

7 Responses

  1. Hans Georg Lundahl says:

    Have you considered that with prolonged cohabitation, the imperfection is done away with when it comes to adulterous acts of a “remarriage”?

    If not all, at least some.

  2. josé alvarado says:

    Well, the ghost writer was not Aquinas, but Victor Fernandez https://cruxnow.com/commentary/2017/01/15/ethicist-says-ghostwriters-role-amoris-troubling/
    Catechism of the Catholic Church 1756 proves Francis and his apologists wrong. Adultery is not any sort of sin and in this case, we are not talking an isolated sin, an occasional one, but the firm decision to live in adultery. Here it is what the Catechism teaches, so sad that Francis forgot it: 1756 “It is, therefore, an error to judge the morality of human acts by considering only the intention that inspires them or the circumstances (environment, social pressure, duress or emergency, etc.) which supply their context. There are acts which, in and of themselves, INDEPENDENTLY OF CIRCUMSTANCES AND INTENTIONS, ARE ALWAYS GRAVELY ILLICIT BY REASON OF THEIR OBJECT; such as blasphemy and perjury, murder and ADULTERY. ONE MAY NOT DO EVIL SO THAT GOOD MAY RESULT FROM IT”.

    • Brian Killian says:

      You are confusing the objective order of morality and the subjective order of guilt. Pope Francis is not claiming that adultery is moral, but that not every couple is guilty of committing it and that he wants communion to be received by everyone that is subjectively capable of receiving it. It’s no different than Aquinas when he says that a generically mortal sin can become a venial sin due to the same kind of mitigating circumstances described in Amoris Laetitia.

      • josé alvarado says:

        The ghostwriter was not Aquinas who never taught what Fernandez teaches via Bergoglio. What we have in AL is Fernandez’s interpretation of Aquinas, not Aquinas. Francis could not quote a single biblical text or church father to support his new teaching on adultery and communion, simply because his innovation is not supported by the Bible and apostolic Tradition, he does not behave like a Catholic. Yes he can quote Kasper and Hunermann, but they are the fruit or a cause of the current state of the German church: only 16.2 of german catholics believe that God is a personal being, 50% of priests do not pray or go to confessión, 40% of german catholics are thinking about leaving the church, the bishops are so permissive and Reinhard Marx is one of Francis´ consultants. Yes, Bergoglio is drinking not from Aquinas, but from the polluted waters of German liberalism and he wants to apply to the whole Church the German recipe for disaster.
        Luther taught that one Christian could not lose salvation even if he commits adultery thousands of times and Francis’ innovation reminds me that letter to Melanchthon alot. Fernandez and Bergoglio do not take seriously what the Catechism teaches on discernment and about adultery. We are not dealing about a single act of adultery committed by a pagan, no one gets civilly remarried without knowing that what he does is adultery, I am talking about a Catholic who had the clarity of will and mind to get married validly in the Church and to rule out that is the lustful desire that does not let him see the gravity of his sin is to be very candid. Blindness caused by sin does not exculpate that catholic, it makes him more guilty. 1756 is very clear adultery IS ALWAYS A GRAVE ILLICIT SIN, and to say “yes I know the commmandment, but I do not see the harm and I am commiting” is a very dangerous new rule. Apply it to homicide…

  1. February 23, 2018

    […] we know that weakness can make mortal sin to become venial, as Aquinas teaches. Therefore, not being in full harmony objectively with God’s law does not necessarily prevent […]

  2. April 27, 2018

    […] Church’s understanding of human weakness is that, as Aquinas taught, it can make mortal sins to become venial ones due to the imperfection of the act. Grave matter is […]

  3. May 30, 2018

    […] subjective freedom and culpability is far from a new idea, it goes back at least as far as St. Thomas Aquinas and is well founded in the Tradition. For example, the CDF, under Saint John Paul II, issued a […]

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