ascertain

verb

1. (transitive)To find out definitely; to discover or establish.

   “As soon as we ascertain what the situation is, we can plan how to proceed.”

   ““There the cause of death was soon ascertained ; the victim of this daring outrage had been stabbed to death from ear to ear with a long, sharp instrument, in shape like an antique stiletto, which […] was subsequently found under the cushions of the hansom.[…]””

   “Walk the dog in the pounding rain / Looking for a way out of my brain, trapped in it / But I cannot ascertain that I'm trapped in it / Or that the traps even real so I remain trapped in this chambers”

   “"[…] On the 18th of October, 1841, a very intense magnetic disturbance was recorded, and amongst other curious facts mentioned is that of the detention of the 10:05pm express train at Exeter for 16 minutes, as from the magnetic disturbance affecting the needles so powerfully, it was impossible to ascertain if the line was clear at Starcross. The superintendent at Exeter reported the next morning that someone was playing tricks with the instruments, and would not let them work."”

2. (obsolete, transitive)To make (someone) certain or confident about something; to inform.

   “Therfore the saide cõmissioners shall mowe say that nowe late during the parlement the King ascertaigned of the saide maliciouse pʳpose of his enemys, willed and desired the lords being then present to shewe their̃ good willes aide and helpe for the saide rescues[…]”

   “We would most gladly ye came yourself if that ye may […] praying you to ascertain us of your News.”

   “Muncer Assured them, that the design was approved of by Heaven, and that the Almighty had in a dream ascertained him of its success.”

3. (Yorkshire, dated, intransitive)To look for something lost.
4. (archaic, transitive)To establish, to prove.

   “The two firſt lines of the following book ſeem to aſcertain the true meaning of the concluſion of this, and to prove ſufficiently that by Ωκεανός here, Homer could not poſſibly intend any other than a river.”

   “In 1695 he [Walter Moyle] was chosen to represent the borough of Saltash in parliament ; a circumstance which ascertains the piece before us to have been written subsequent to that period.”

   “We must look somewhat deeper would we learn why a book which now tries our patience was not undeserving of those multiplied editions which have ascertained its popularity.”

5. (archaic, transitive)To ensure or effect.

   “It is true, that no diligence can aſcertain ſucceſs ; death may intercept the ſwifteſt career ; but he who is cut off in the execution of an honeſt undertaking, has at leaſt the honour of falling in his rank, and has fought the battle, though he miſſed the victory.”

   “The ministry, in order to ascertain a majority in the house of lords, persuaded the queen to take a measure which nothing but necessity could justify.”

   “On the contrary, the Squire’s influence as a man of family and property, in the immediate neighbourhood, who actually kept greyhounds, and at least talked of hunters and races, ascertained him the support of the whole class of bucks, half and whole bred, from the three next counties ; and if more inducements were wanting, he could grant his favourites the privilege of shooting over his moors, which is enough to turn the head of a young Scotchman at any time.”