There are also two kinds of Truths, those of Reasoning and those of Fact. The Truths of Reasoning are necessary, and their opposite is impossible. Those of Fact, however, are contingent, and their opposite is possible. When a truth is necessary, the reason can be found by analysis in resolving it into simple ideas and into simpler truths until we reach those that are primary. In other words, he is the source of whatever there is real in the possible.
Souls act in accordance with the laws of final causes through their desires, ends and means.
Bodies act in accordance with the laws of sufficient causes or of motion. It does not seem possible for all possible things to exist, they get in one another's way.