St. Thomas defines a dialectical as opposed to demonstrative discourse as one that uses some being of the mind to define the subject under consideration. But he is also clear that at least three things needs to be defined with some being of reason: persons, time and motion.
The person needs to be defined with the intentional category individual or particular, each of which are second intentions opposed to species or universal. Time is a sort of measure, and so presupposes some contribution from the one measuring, i.e. he has to specify some moment that will count as “before”. Motion too requires some contribution of the subject, since it exists relative to the terms of the mobile, but when these terms are realized the thing is not in motion. Motion and time are both dependent on the cognition of higher animals – without memory and anticipation we have neither time nor motion but only, says St. Thomas, “an imperfect existence”. Even to say this might go too far, since the being is only “imperfect” in relation to the very term which depends on memory and anticipation to exist; and the “existence” spoken of is not a formal concept of the sort that a metaphysician could do something with but only a way of gesturing at something or other.