After the verb yam 'to give', preceded by upa , when used in the sense of 'espousing', the ātmanepada is used.,
This is clear. As भार्यामुपयच्छते 'he espouses or knows his wife.' But not so when another's wife is meant; there it is parasmaipadi.
By rule 1.3.78, the verb yam would have been parasmaipadi, but the present sutra makes an exception, when the root takes the preposition upa and means \to marry, to espouse, or to accept.\ The meaning of sva-karana is confined to accepting in general. This is according to Kasika; according to Mahabhashya, sva-karana means to make one's own what was not previously his own.
Why do we say in the sense of \marrying\? When it has any other sense, parasmaipada affixes will be employed, as देवदत्तो यज्ञदत्तस्य भार्यामुपयच्छति, Devadatta has illicit intercourse with the wife of Yajnadatta.',