In a way that can be clearly shown or proved; in a manner that is evident or provable.
From demonstrable + -ly (adverb-forming suffix). This transforms the adjective into an adverb indicating the manner in which something is shown or occurs.
When you say something is 'demonstrably false,' you're making a promise that you can prove it—so the word carries confidence and certainty, which is why lawyers and scientists love using 'demonstrably' to sound authoritative.
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