一直以嚟，西方哲學界對知識嘅定義包含咗三個要素，亦即係「得到證成嘅真信念」，英文中通常被簡稱為JTB理論。具體嚟講，當A“知道”（know）事件B時，或者叫「A已經掌握B嘅知識」，就可以做以下嘅論證：
For a long time, the definition of knowledge in Western philosophical circles has included three elements, that is, "proven true beliefs", which is often referred to as JTB theory in English. Specifically, when A "knows" about event B, or "A already has knowledge of B", the following argument can be made: