The legality of power must be estimated not by what it will do, but by what it can do.

Explanation

(English-origin maxim.) Power must be judged by its potential reach, not merely its present exercise — a power that can be abused is dangerous even when it has not yet been abused.

Where this applies

• A statute grants an official broad discretion, and a citizen challenges the power itself, not just how it was used.
• A government defends a sweeping authority by promising to use it only reasonably.