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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.


  • (UK) IPA(key): /ˌæsəˈteɪn/
  • (US) enPR: ăs'-ər-tānʹ, IPA(key): /ˌæsɚˈteɪn/
  • (file)
  • Rhymes: -eɪn
  • Hyphenation: as‧cer‧tain


ascertain (third-person singular simple present ascertains, present participle ascertaining, simple past and past participle ascertained)

  1. To find out definitely; to discover or establish.
    Synonyms: determine, discover, establish, find out, learn, work out
    As soon as we ascertain what the situation is, we can plan how to proceed.
    • 1904–1905, Baroness Orczy [i.e., Emma Orczy], “The Tremarn Case”, in The Case of Miss Elliott, London: T[homas] Fisher Unwin, published 1905, →OCLC; republished as popular edition, London: Greening & Co., 1909, OCLC 11192831, quoted in The Case of Miss Elliott (ebook no. 2000141h.html), Australia: Project Gutenberg of Australia, February 2020:
      “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. []
    • 2023, “Split The Atom”, in Kae Tempest (lyrics), Nice Idea:
      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
    • 2023 November 15, Prof. Jim Wild, “This train was delayed because of bad weather in space”, in RAIL, number 996, page 30:
      " [] 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) To make (someone) certain or confident about something; to inform.
    • 1436, Sir Nicholas Harris Nicolas, editor, Proceedings and Ordinances of the Privy Council of England, volume IV, published 1835, page 352c:
      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 []
    • 1844 [1483], Caroline A. Halsted, quoting Richard III, chapter XV, in Richard III as Duke of Gloucester and King of England, page 307:
      We would most gladly ye came yourself if that ye may [] praying you to ascertain us of your News.
    • 1769, William Robertson, “The History of the Reign of the Emperor Charles V”, in George Gleig, editor, The Historical Works of William Robertson, volume V, Edinburgh: Doig & Stirling, published 1813, page 395:
      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. (archaic) To establish, to prove.
    • 1791, William Cowper, Homer’s Odyssey, volume II, book XI, page 274 (footnote):
      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.
    • 1800, Edward Malone, The Critical and Miscellaneous Prose Works of John Dryden, volume III, London: H. Baldwin and Son, page 382 (note 8):
      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.
    • 1842, Isaac D'Israeli, “The Ship of Fools”, in Amenities of Literature: Consisting of Sketches and Characters of English Literature, volume I, Paris: Baudry, page 254:
      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.
  4. (archaic) To ensure or effect.
    • 1751 June 29, Samuel Johnson, The Rambler[1], volume III, number 134, London: A. Millar et al., published 1761, page 155:
      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.
    • 1757–65, Tobias Smollet, chapter X, in The History of England from the Revolution to the Death of George II, volume II, London: Richardson & Co., published 1830, page 224:
      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.
    • 1824, Sir Walter Scott, “Administration”, in St. Ronan's Well, Boston: Samuel H. Parker, page 29:
      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.

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