先驗（拉丁語： ；也譯作先天）喺拉丁文入面指“嚟自先前嘅嘢”，或者引申去“有經驗之前”。喺近代西方傳統入面，認為先驗指無需經驗或者先於經驗獲得嘅知識。佢通常同埋後驗知識去比較，後驗指嘅就係“有經驗之後”，亦即"需要經驗"。呢種區分嚟自於中世紀邏輯所區分嘅兩種論證，從原因到結果嘅論證叫做“先驗”，而從結果到原因嘅論證就叫做“後驗”（拉丁語： ）。
A priori (Latin : ; also translated as innate) in Latin refers to uranium from something that came from the past, and perhaps by extension to go back to the pre-empirical anger. In the modern Western tradition, a priori is considered to refer to knowledge that is acquired without experience or perhaps prior to experience. He usually compares it to posterior knowledge, which refers to retrospective empirical uranium, i.e., uranium requires empirical uranium. This distinction derives from the distinction between two kinds of arguments in medieval logic, the argument from cause to effect is called "a priori", and the argument from effect to cause is called "a posteriori" (Latin: ).