ascertain
v.v. to find out the true facts about something. You use this when you need to be sure about a piece of information.
v. to find out something with certainty; to determine through investigation or examination.
We need to ascertain the cause of the problem.
The police are still trying to ascertain the exact time the accident occurred by checking security cameras.
Before the board can approve the merger, they must ascertain whether the company's current debts will impact long-term profitability.
From Middle English acerteynen, from Old French acertener, from a- (“to, towards”) + certener (“make sure of”), from the adjective certain, from Latin certus (“certain, fixed”). Compare to Spanish acertar.
The verb is transitive and often followed by a 'that' clause or a 'wh-' clause (e.g., 'ascertain whether', 'ascertain how').