Definition of "have to"

have to

/ˈhæv.tuː/

verb
third-person singular simple present has to, present participle having to, simple past and past participle had to
1. Must; need to; urged to; to be required to. Indicates obligation.
  Quotations
  I was about to say that I had known the Celebrity from the time he wore kilts. But I see I will have to amend that, because he was not a celebrity then, nor, indeed, did he achieve fame until some time after I left New York for the West.
  1897 December (indicated as 1898), Winston Churchill, chapter I, in The Celebrity: An Episode, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd.
  Energy has seldom been found where we need it when we want it. Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame.
  2013 July-August, Henry Petroski, “Geothermal Energy”, in American Scientist, volume 101, number 4
2. (with be) Must (logical conclusion).