The ideas of causality and natural law lead directly to the concept of metaphysical possibility. Whatever action is consistent with the nature of an acting entity is metaphysically possible; whatever action is not consistent with its nature, is metaphysically impossible for that entity. For example, it is possible for a woman to err, since she has the natural capacity of choice. Assuming that she is not in a coma or other special circumstances, it is also possible for her to think. It is not in general possible for her to evade the consequences of her errors, since she has a specific nature and must interact with other persons and things that have a specific nature. For example, if she ingests a poison, it may become metaphysically impossible for her to escape imminent death. Her "free will" is not a license enabling her to evade natural law.

As noted previously (pp. 1.3:74-6), metaphysical possibility must not be confused with epistemological possibility, which refers to an one's state of knowledge about some hypothesis.