Time and Existence

The different meanings of the word "to be" have interested philosophers at least since Aristotle. In my paper, I would like to draw attention to the following question: in what way "to be", when predicating actual existence of an individual, is connected with time and how it refers to the individual and its real change. I want to do this by presenting Thomas Aquinas' interpretation of the Aristotelian analysis of the different means of the word "to be" referring to Peter Geach, who discussed this doctrine in relation to the interpretation of "existence" by Russell and Quine. My aim is to ask whether this medieval doctrine may contribute to the clarification of the relation between unity and time with regard to the question of endurantism and perdurantism.