throw the baby out with the bathwater

• throw out the baby with the bathwater, throw out the baby with the bath water, throw the baby out with the bath water

From a calque of German schüttet das Kind mit dem Bade aus, a proverb that dates to 1512. First recorded by Thomas Murner in his satire Narrenbeschwörung. First appeared in English when Thomas Carlyle translated it and used it in an 1849 essay on slavery.

• (Received Pronunciation) IPA^(key): /θɹəʊ ðə ˈbeɪbi aʊt wɪð ðə ˈbɑːθwɔːtə(ɹ)/
• (General American) IPA^(key): /θɹoʊ ðə ˈbeɪbi aʊt wɪθ ðə ˈbæθwɔtɚ/

• Audio (General Australian):

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throw the baby out with the bathwater (third-person singular simple present throws the baby out with the bathwater, present participle throwing the baby out with the bathwater, simple past threw the baby out with the bathwater, past participle thrown the baby out with the bathwater)

1. (idiomatic) To discard, inadvertently or through overzealousness, something valuable or essential ("the baby") in the process of removing or rejecting something unwanted or undesirable ("the bathwater").

   They cancelled the entire project because the new management didn't like the prototype, but I think they threw the baby out with the bathwater.

• “Don't throw the baby out with the bathwater”, in BBC Learning English, BBC, 14 October 2014