Thomas Aquinas,
Summa Theologiae — Question 154 - OF TEH PARTS OF LUST…
“ Wherefore simple fornication, which is committed without injustice to another person, is the least grave among the species of lust. Then, it is a greater injustice to have intercourse with a woman who is subject to another's authority as regards the act of generation, than as regards merely her guardianship. Wherefore adultery is more grievous than seduction. And both of these are aggravated by the use of violence. Hence rape of a virgin is graver than seduction, and rape of a wife than adultery. ”
