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can't help

Also, can't help but or cannot but. Be unable to do otherwise. For example, I can't help thinking that the keys will turn up eventually, or He couldn't help but believe he would pass the entrance exam, or I cannot but applaud his efforts. The first of these phrases, can't help, is always followed by a present participle whereas the others take an infinitive. [c. 1700]

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.