Actual extinction is a thing's ceasing to exist in fact.
Possible extinction means a thing could cease to exist by its created nature, even if it is never actually brought to an end.
Paradise and Hell will not actually perish, although, as created things, they are capable of perishing if Allah so willed. Their unending continuance is by Allah's will.
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Paradise and Hell: Their Permanence, and the Decree of Good and Evil
Actual extinction is a thing's ceasing to exist in fact.
Possible extinction means a thing could cease to exist by its created nature, even if it is never actually brought to an end.
Paradise and Hell will not actually perish, although, as created things, they are capable of perishing if Allah so willed. Their unending continuance is by Allah's will.