Tertullian was much indebted to Stoic metaphysics. For the most part, he chose to utilize the four Stoic categories of being rather than the well-known ten ontological predicates of Aristotle. One category of Stoic metaphysics is relative disposition. Stoic relative states or dispositions differ somewhat from Aristotelian relations in that the Stoics do not think a specified entity’s particular constitution as such is dependent on its corresponding relative state. All that relative dispositions tell us (according to the Stoic thinkers) is how some particulars relate to other particulars in the world. The Stoics do not believe that the constitution of one relative state qua relative state is dependent on its being “toward something” (ta pros ti). As Catherine Lacugna explains, “In the case of the father-son relation, if the child dies, the man ceases to be a father but he does not cease to exist. By contrast, in the use made by theologians of Aristotelian philosophy, a father is constituted as father by his son, and vice versa.” Similarly, in the Greek Trinitarian tradition “relation will show only how, but not what, something is.” On the other hand, ancient Latin trinitarians generally perceived the triune relations as constituting the persons, making them what they are, as opposed to Greek thought, which suggests that relata simply manifest the mode wherein the three divine persons subsist.
Tertullian, although he is a Latin theologian, nonetheless favors the Stoic and eastern Christian understanding of relations as being ta pros ti in the world without necessarily thinking that one relative disposition constitutes another relation ontologically. He clearly relied on the metaphysical categories of the Stoics. That is probably why Tertullian could coherently argue that while God is eternal or everlasting, there was a time when the Son as such or the Father as such did not exist even though God is from eternity to eternity (Psalms 90:2). The relative dispositions (in Tertullian’s estimation) do not constitute the divine persons qua persons.