“Mental”: this is when something is presented to the mind and its impossibility is not known. One then says, “This is possible,” not because one knows it to be possible, but because one does not know it to be impossible—even though it may be impossible in external reality.

“External”: this is when something is known to be possible in external reality. Such knowledge comes from knowing that the thing itself exists, that something comparable to it exists, or that something further removed from existence than it exists. If that which is further removed from existence actually exists and is therefore possible, then that which is nearer to existence is all the more possible. This is the Quran’s method of demonstrating “the possibility of resurrection.”

It demonstrates this in several ways. Sometimes Allah tells of those whom He caused to die and then brought back to life, as He tells of the people of Moses who said:

“Show us Allah openly.”

He says:

“So the thunderbolt seized you while you looked on.”

“Then We raised you up after your death.”

He also tells of:

“Those who left their homes in their thousands, fearing death. Allah said to them, ‘Die’; then He brought them back to life.”

And of:

“Or like the one who passed by a town that had fallen in upon its roofs. He said, ‘How will Allah bring this back to life after its death?’ So Allah caused him to die for a hundred years, then raised him up.”

And of Abraham, when he said:

“My Lord, show me how You give life to the dead”—and the rest of the account.

Likewise, He tells of the Messiah, who used to bring the dead to life by Allah’s permission, and of the Companions of the Cave, who were awakened after three hundred and nine years.

At other times, He demonstrates this through the first creation, for bringing something back is easier than creating it in the first place, as in His words:

“If you are in doubt about the resurrection, then indeed We created you from dust”—and the rest of the verse.