P29: Whatever the Mind understands under a species of eternity, it understands not from the fact that it conceives the Body’s present actual existence, but from the fact that it conceives the Body’s essence under a species of eternity.

Dem.: Insofar as the Mind conceives the present existence of its Body, it conceives duration, which can be determined by time, and to that extent it has only the power of conceiving things in relation to time (by P21 and IIP26). But eternity cannot be explained by duration (by ID8 and its explanation). Therefore, to that extent the Mind does not have the power of conceiving things under a species of eternity.

But because it is of the nature of reason to conceive things under a species of eternity (by IIP44 C2), and it also pertains to the nature of the Mind to conceive the Body’s essence under a species of eternity (by P23), and beyond these two, nothing else pertains to the Mind’s essence (by IIP13), this power of conceiving things under a species of eternity pertains to the Mind only insofar as it conceives the Body’s essence under a species of eternity, q.e.d.

Schol.: We conceive things as actual in two ways: either insofar as we conceive them to exist in relation to a certain time and place, or insofar as we conceive them to be contained in God/Nature and to follow from the necessity of the divine/universal nature. But the things we conceive in this second way as true, or real, we conceive under a species of eternity, and to that extent they involve the eternal and infinite essence of God/Nature (as we have shown in IIP45 and P45 S).