Well, you can speak honestly regardless of whether what you say is true.
It’s the level of falsification you apply and the warranty you put behind it.
Honest > Truthful > True > Analytically True > Tautological.
Honest(personal but not instrumental due diligence complete) > Truthful(instrumental Due diligence complete) > True(proper) > Analytic Truth(math, logic) > Tautological.
Man of us are honest, truthfulness takes time and effort, we rarely if ever know what’s true due to informational incompleteness, and tautology is meaningless repetition.