Qui tacet consentire videtur, ubi loqui debuit ac potuit.
"Who is silent, when he ought to and might have spoken, is seen to agree."
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This is really just a rephrasing of the old Latin rule of law: "qui tacet consentire videtur (one who is silent is seen to have given consent)." To acquiesce is to accept or to comply. So, it follows that if a person chooses silence as a response, then that is interpreted (rightly or wrongly) as acceptance.