Summa Contra Gentiles

by Thomas Aquinas

Book III, Chapter 122

THE REASON WHY SIMPLE FORNICATION IS A SIN ACCORDING TO DIVINE LAW,
AND THAT MATRIMONY IS NATURAL

Thomas AquinasIn this chapter Thomas discusses the morality of fornication.

Since Thomas bases his argument on the legitimacy or not of “the emission of male seed”, the text is at times quoted to prove the alleged sinfulness of using contraceptives in marriage.

Such conclusions are, however, inadmissable because (1) Thomas did not know the correct biological facts and (2) he did not know the circumstances of marriage in our own times. See below for a fuller commentary.