The four real relationships that exist among the persons in the Trinity. There is the relation of the Father to the Son as active generation or paternity; the relation of the Son to the Father as passive generation or filiation; the relation of the Father and the Son to the Holy Spirit as active spiration; and the relation of the Holy Spirit to the Father and the Son as passive spiration.
Although there are four real relationships within the Trinity, only three stand in contrast to one another and are therefore really distinct, namely the fatherhood, sonship, and the passive spiration. Active spiration stands in contrast only to passive spiration but not to the fatherhood and sonship. Consequently it is not really but only virtually distinct from the fatherhood and sonship. However, the relations in God are really identical with the divine nature.