The first two Ways relate to causation. When Aquinas argues that a causal chain cannot be infinitely long, he does not have in mind a chain where each element is a prior event that causes the next event; in other words, he is not arguing for a first event in a sequence. Rather, his argument is that a chain of "concurrent" or "simultaneous" effects must be rooted ultimately in a cause capable of generating these effects, and hence for a cause that is first in the hierarchical sense, not the temporal sense.