Whether the condition of slavery is an impediment to matrimony?

Objections

Objection 1 : It would seem that the condition of slavery is no impediment to matrimony. For nothing is an impediment to marriage except what is in some way opposed to it. But slavery is in no way opposed to marriage, else there could be no marriage among slaves. Therefore slavery is no impediment to marriage.
Objection 2 : Further, that which is contrary to nature cannot be an impediment to that which is according to nature. Now slavery is contrary to nature, for as Gregory says (Pastor. ii, 6), "it is contrary to nature for man to wish to lord it over another man"; and this is also evident from the fact that it was said of man (Gn. 1:26) that he should "have dominion over the fishes of the sea," but not that he should have dominion over man. Therefore it cannot be an impediment to marriage, which is a natural thing.
Objection 3 : Further, if it is an impediment, this is either of natural law or of positive law. But it is not of natural law, since according to natural law all men are equal, as Gregory says (Pastor. ii, 6), while it is stated at the beginning of the Digests (Manumissiones, ff. de just. et jure.) that slavery is not of natural law; and positive law springs from the natural law, as Tully says (De Invent. ii). Therefore, according to law, slavery is not an impediment to any marriage.
Objection 4 : Further, that which is an impediment to marriage is equally an impediment whether it be known or not, as in the case of consanguinity. Now the slavery of one party, if it be known to the other, is no impediment to their marriage. Therefore slavery, considered in itself, is unable to void a marriage; and consequently it should not be reckoned by itself as a distinct impediment to marriage.
Objection 5 : Further, just as one may be in error about slavery, so as to deem a person free who is a slave, so may one be in error about freedom, so as to deem a person a slave whereas he is free. But freedom is not accounted an impediment to matrimony. Therefore neither should slavery be so accounted.
Objection 6 : Further, leprosy is a greater burden to the fellowship of marriage and is a greater obstacle to the good of the offspring than slavery is. Yet leprosy is not reckoned an impediment to marriage. Therefore neither should slavery be so reckoned.