后此谬误（拉丁语：post hoc）或后此故因此（拉丁语：post hoc ergo propter hoc；英语：after this, therefore because of this），又称巧合关系（英语：coincidental correlation），是逻辑学研究中经常遇到的认识错误。它是指这样一种不正确的推理：如果A事件先于B事件发生，A事件则是B事件的原因。

观察到事件A在事件B之前的事实，并不证明事件A是事件B的原因。认为“在此事件之后”便意味着“因为此事件”就是犯了后此谬误。

Post hoc ergo propter hoc (Latin: "after this, therefore because of this") is a logical fallacy (of the questionable cause variety) that states "Since event Y followed event X, event Y must have been caused by event X." It is often shortened to simply post hoc fallacy. It is subtly different from the fallacy cum hoc ergo propter hoc ("with this, therefore because of this"), in which two things or events occur simultaneously or the chronological ordering is insignificant or unknown. Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality. The fallacy lies in coming to a conclusion based solely on the order of events, rather than taking into account other factors that might rule out the connection.