Adultery Without an Affair? The Sin of Mental Adultery

What does it really mean to commit adultery in the heart? This article offers deeper Catholic clarity on mental adultery, explaining when lustful thoughts or sexual fantasies become sinful and how spouses can better understand the call to purity, fidelity, and marital love.

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Most people, even those outside the Church, recognize that adultery is one of the most pernicious evils that plague our society, and it is one that brings chaos and wreckage to countless marriages. As Christians, however, we are not only called to avoid the physical act of sleeping with someone other than our spouse, but we are also called to avoid even interior acts of sexual pleasure toward anyone who is not our lawful spouse. This, however, raises various moral questions. 

That is, even if spouses are not in any way pursuing an actual sexual relationship with a third party, how should they concretely morally evaluate willfully entertained sexual thoughts, desires, or looks that do not pertain to their spouse? Do these sins constitute adultery properly so-called? Would they be grounds for separation in the same way that physical adultery would be? 

These are questions we hope to address in this article. To answer these questions, we should first articulate a principle that undergirds the moral relationship between thought and external action in any domain. That is, the morality of any willfully entertained thought ultimately stems from the moral character of the object of the thought so entertained. This is because, as St. Thomas Aquinas reminds us, whenever the mind entertains some object of thought for its consideration, in some mysterious way, a real union between mind and mental object takes place. In the Gospel of Luke, this relationship is brought to light when the Blessed Virgin euphemistically refers to Her sacred virginity as consisting in the fact that She “knows not” man. In other words, there is something truly analogous between the intimacy between mind and mental object on the one hand and conjugal union on the other. I’m sure this is an analogy that will not be lost on any of our readers. This is why, for example, when the Israelites abandoned God’s covenant for their idols, this betrayal is likened to the sin of adultery in particular because there is something fundamentally irreconcilable about the soul and its faculties being caught between two contrary objects of love. This is also why one mortal sin has the power to rob us of our eternal salvation, for the Blessed Trinity will not and cannot abide within the life of a soul that has chosen a directly contrary object for its object of love. 

All of this is to illustrate the fact that, as Christ Himself famously teaches in the Gospel of Matthew, mental adultery stems from precisely the same disposition of a heart as physical adultery, which is a disposition that has already fundamentally wandered away from the person towards whom he or she has been sacramentally ordained. 

With this being said, there are some practical caveats and nuances that should be articulated. For one, while both mental adultery and physical adultery stem from the same disposition of the heart and share in the same gravity of malice, they are still different acts and impact marriage differently. Whereas mental adultery (or, perhaps, pornography usage) does betray spousal trust and must be addressed through confession and spousal reconciliation and healing, physical adultery desecrates more directly and straightforwardly the very act which constitutes the marriage bond itself. Therefore, if all a spouse is guilty of is solitary acts of adulterous sexual pleasure, then I would not maintain that this would be grounds for spousal separation in the same way that physical adultery is by its nature. There are also other instances where the lines of mental adultery could potentially become blurred. Let’s entertain a couple scenarios. 

Scenario: A husband enjoys sexual fantasies about his wife in his own mind, but the phantasms (mental images) of his wife start to morph into the likenesses of other women. In this case, once the likeness of the woman he is imagining no longer retains the characteristic traits of his wife which allow him to recognize the woman as his wife, he should, once he realizes this is happening, deliberately reorient his thoughts backward or even refrain from lingering on these thoughts altogether. 

Scenario: As part of a sexual fantasy, spouses want to imagine each other during intimacy as different celebrities or fictional characters to spice things up. This would be mortally sinful. While spouses could imagine each other as filling in for fictional characters within a fantasy, to imagine their spouse as someone with unrecognizably different physical or facial characteristics than their spouse has by nature would be to take sexual pleasure in someone other than their spouse which is strictly speaking an adulterous act. 

In these and any other scenario, the line is crossed whenever we entertain any sexual thoughts or desires about someone we do not truthfully recognize as our lawful spouse, the one the Lord through His sacrament of matrimony has ordained us to love and to cherish for the rest of our earthly lives.