Many years ago I read that a certain theologian said fornication with a more beautiful woman is less sinful than with an uglier one. Which medieval theologian was this, and how did he argue his position? (His position was a minority position.)
Alan of Lille (†1203), Liber pœnitentialis 1.27:
<XXVII> Utrum pulchra fuerit vel turpis?
Considerandum est etiam utrum pulchra fuerit vel non, quia minus peccat qui cognoscit pulchram quam qui turpem; quia ille magis cogitur qui pulchram: ubi major coactio, ibi minus peccatum.
27. Whether she was beautiful or ugly?
It must also be considered whether she was beautiful or not, because one who knows a beautiful [woman] sins less than [one who knows] an ugly [woman]; because he who [knows] the beautiful [woman] is more forced: where there is more coercion/force, there is less sin.
p. 196 of: Alan of Lille and J. Longère, “Liber pœnitentialis: Les Traditions Moyenne et Courte,” Archives d’histoire Doctrinale et Littéraire du Moyen Âge 32 (1965): 169–242, cited in Elliott Spiritual Marriage p. 126n11.
He seems to be assuming that fornication with an ugly woman would require a more deliberate act of the will, as though the will becomes less voluntary by being attracted to its object, the good and beautiful. But this isn't true; St. Thomas Aquinas, Summa Theologica I-II q. 6 a. 7 co.:
Concupiscence does not cause involuntariness, but on the contrary makes something to be voluntary. For a thing is said to be voluntary, from the fact that the will is moved to it. Now concupiscence inclines the will to desire the object of concupiscence. Therefore the effect of concupiscence is to make something to be voluntary rather than involuntary.