presupposition
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/ˌpriːsʌpəˈzɪʃn/
🇬🇧
/ˌpriːsʌpəˈzɪʃn/
A belief or idea that you think is true without having proof, which is used as a starting point for further discussion or argument.
His argument had a basic presupposition that all planets have circular orbits.