Some argue that this is possible because we do not know it to be impossible, unlike things whose impossibility is evident, such as a body’s being both moving and stationary. This resembles the argument some advance that a proposition is not self-evident because other self-evident propositions are clearer than it. This is a weak argument, for a self-evident proposition is one that reason affirms with certainty once its subject and predicate are conceived. Yet these two concepts may themselves be obscure. Propositions therefore differ in clarity and obscurity according to how clearly they are conceived, just as they differ according to differences between minds. This does not undermine their being known without inference, nor does it follow that whatever has not been shown to be impossible must be possible.

Indeed, the former claim is weaker still, for something may be impossible because of hidden consequences that it necessarily entails. Unless it is known that those consequences do not obtain, or that they are not necessarily entailed, its possibility cannot be affirmed with certainty. Impossibility here encompasses both what is impossible intrinsically and what is impossible owing to something else. Mental possibility is, in reality, the absence of knowledge of impossibility; but not knowing something to be impossible does not entail knowing it to be possible in external reality. Rather, the mind remains without knowledge either of its impossibility or of its possibility in external reality. This is mental possibility.

For Allah, glorified and exalted is He, did not content Himself with this when explaining the possibility of resurrection: something may be impossible—even owing to something else ن—although the mind does not know it to be impossible. Possibility in external reality is different: once it is known, impossibility is ruled out.

A person knows that something is possible in external reality:
sometimes by knowing that it exists, and sometimes