1969年，凱斯·雷爾（ ）同埋湯馬斯·帕克森提出咗一個新嘅條件：可敗性條件。佢噉樣定義：一個命題係可以擊敗嘅，只要知道咗另一個事實就有可能將佢否決。但知識係唔可以擊敗，因為有得到辯護嘅真信念。亦即係話，無論點樣再得到其他嘅真命題，得到辯護嘅真信念係唔會畀人否定。
In 1969, Keith · Reel ( ) and Thomas · Paxson proposed a new condition: the defeat condition. He defined it this way: a proposition can be defeated, and it is possible to reject it if another fact is known. But knowledge cannot be defeated, because the true faith that has been defended has been obtained. That is to say, no matter how much other true propositions are obtained, the true conviction that is defended cannot be denied.