as ‧ cer ‧ tain /ˌæsəˈteɪn $ ˌæsər-/ BrE AmE verb [intransitive and transitive]
[ Date: 1500-1600 ; Language: Old French ; Origin: acertainer , from certain ]
formal to find out something SYN establish :
A postmortem was ordered to try to ascertain the cause of death.
ascertain whether/what/how etc
Tests were conducted to ascertain whether pollution levels have dropped.
ascertain that
Police had ascertained that the dead man knew his killer.
ascertain something from somebody/something
You should ascertain the level of insurance cover from the car rental company.
—ascertainable adjective
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Ascertain is used mainly in formal or technical contexts. In everyday English, people usually say find out :
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We need to find out exactly what happened before we jump to any conclusions.