Adultery and other kinds of act contrary to the good of marriage

In this extract from Stanford encyclopaedia the author argues that Aquinas sees sex within marriage as exclusive because it is the key to human and social flourishing (eudaimonia).  The right kind of sex int he right place (marriage) builds an excellent life – personal and social. PB

http://plato.stanford.edu/entries/aquinas-moral-political/#SupMorPri

Marriage is, Aquinas says, a primary human good and, philosophically considered, it has a dual point (end, finis): (i) the procreation and bringing up of children is a manner suited to their good, and (ii) fides, which goes far beyond the literal translation “faithfulness” and includes not only exclusivity and permanence but also the positive readiness and commitment to being united with one’s spouse in mind, body and domestic life based on helping one another. Aquinas neither subordinates one of these two “ends” to the other, nor regards it as appropriate to choose to divide them. Fides is a good and sufficient reason for engaging in the usus matrimonii, the kind of sexual act that is intended to enable both husband and wife to experience and in a particular way realise the good of their marriage, so that the act’s delight is token of their commitment.

Consequently the kind of wrongful sexual choice most often considered by Aquinas is engaging in intercourse with one’s spouse without fides, because one either (i) is thinking of one’s spouse in the way one would think of a prostitute, or (significantly worse) (ii) would be willing to have sex with somebody else if some other attractive person were to be available. Such depersonalized sex acts are instances of willing against the good of marriage (contra bonum matrimonii).  Another example, in itself much more serious, is a married person’s choice to have intercourse with some third party (perhaps with the other spouse’s consent). All other wrongful kinds of sex act are wrong not because they are unnatural in some biological or sociological sense of “unnatural”, but because they are against reason’s directive to respect, if not also pursue, the good of marriage, a respect that requires us to keep the pursuit of sexual satisfaction for marriage (the right kind of sex in the right place).

Unless you see sex before marriage as wrong, your stance about human sex acts is contra bonum matrimonii (against the good of marriage) and unreasonable because one cannot coherently maintain that the intercourse of the married enables them to actualize and experience their fides (faith/faithfulness) and their marriage, a thought essential to the flourishing (bonum) of marriage and thus of children and thus of the wider community as a whole. One measure of the gravity of morally bad sex acts is applicable to some kinds but not others: injustice (as in rape or seduction of the vulnerable). Another measure, applicable to all such acts, is the extent of the deviance (“distance”) between acts of that kind and truly marital acts.

As in ours, many in Aquinas’ milieu found it difficult to understand how mutually agreeable sex could be a serious moral issue, or indeed a moral issue at all. Aquinas noted this, but was clear that every kind of conduct that acts out and thus confirms and reinforces a disposition of will contra bonum matrimonii is seriously wrong because so many aspects of individual and social flourishing profoundly depend upon the health of the institution of marriage, as it exists in the real lives of adults and children. It is worth repeating, since the point is so often misunderstood and misreported, that Aquinas’ moral arguments for distinguishing good from bad sex never run from “natural” to “therefore good/reasonable/right”, but always from “good/reasonable/right” to therefore “natural” (and similarly, of course, for unreasonable and unnatural): see II-II q. 153 a. 2c, a. 3c, q. 154 a. 1c, a. 2 ad 2, a. 11.