Is "Suppose that _ is true; then _ is true" an incorrect usage of suppose? Is "presuppose" supposed to be used here? [closed]
I'm trying to understand what presuppose means, especially as opposed to "assume".
You'd not start a sentence with 'presuppose'.
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Suppose that A is true. Then B follows.
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Suppose that x is an odd number. Then its square is odd too.
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Suppose that many people disobey the social distancing rules. Then a second wave will occur.
You rarely use 'presuppose' other than when the contingent truth / state / goal / theory is also stated, and usually first.
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B being true/the case presupposes that A is true.
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Saying that we will eradicate the virus quickly presupposes that an effective and safe antiviral or vaccine will be discovered and tested quickly.
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The permanent presupposes human foresight. [M-W]
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Darwin’s theory doesn’t presuppose any special direction in evolution. [M-W]
'Presuppose that ...' is unidiomatic.
[edit: Thanks to Jason Bassford for pointing out the additional, rarer sense ('assume as an established fact to further build on'), usually taking a that-clause (possibly with 'that' deleted):
- the book presupposes [that] its readers will already know something about the subject (op cit)
but sometimes with a DO:
- The government cannot pass judgment upon or presuppose the illegitimacy of religious beliefs and practices. [op cit] [very formal; legal/political register] ]
but this sense would be unidiomatic with OP's suggested syllogistic sentence.