An argument follows necessarily in the negative from the not possible to the not being, though not in the affirmative.

Explanation

If a thing is impossible, it necessarily does not exist — but the reverse does not hold, because the mere absence of a thing does not prove its impossibility.

Where this applies

• Just because something does not currently exist does not prove it is impossible.
• The fact that a right is not being exercised does not mean it cannot be exercised.