This study aims at exploring the various semantic effects of the French temporal conjunction Avant que (“before”). It shows how Avant que, as a simple marker of anteriority, reacts to its linguistic context in such a way that new meanings emerge, which cannot be directly attributed to the conjunction. Via a presuppositional analysis that takes into account factual as well as “counterfactual” or “suspensive” readings of Avant que, and through numerous attested examples, it reveals the mechanisms which are responsible for generating specific semantic effects. These effects are divided into three major categories, ranging from preventing (avant que P as “in order that not P” or “in such a way that not P”) to allowing (avant que P as “in order that P”), or deliberating (avant que P as “in order to decide if P”).