as·cer·tain 
/ˌæsɚˈteɪn/ verb
as·cer·tains; as·cer·tained; as·cer·tain·ing /ˌæsɚˈteɪn/ verb [+ obj] formal : to learn or find out (something, such as information or the truth)
▪ They were unable to ascertain [=(more commonly) determine] the cause of the fire. ▪ The police are now attempting to ascertain his whereabouts. [=to find out where he is] ▪ Her doctors have been unable to ascertain [=find out] why she is ill. = Her doctors have been unable to ascertain the cause of her illness. ▪ The information can be ascertained by anyone with a computer.
▪ They were unable to ascertain [=(more commonly) determine] the cause of the fire. ▪ The police are now attempting to ascertain his whereabouts. [=to find out where he is] ▪ Her doctors have been unable to ascertain [=find out] why she is ill. = Her doctors have been unable to ascertain the cause of her illness. ▪ The information can be ascertained by anyone with a computer.
— as·cer·tain·able /ˌæsɚˈteɪnəbəl/ adjective
▪ The cause of the fire was not readily/easily ascertainable.
/ˌæsɚˈteɪnəbəl/ adjective ▪ The cause of the fire was not readily/easily ascertainable.
