当knowledge指一个人对某一具体事物或具体学科的知识时,可以与不定冠词a连用(不管有无定语)
如:He has an wide knowldge of history.
当knowledge泛泛地指知识的时候,它是个不可数名词,不能与不定冠词a连用
如:Knowledge is power.
a knowledge of 指的是比较广泛的某门学科的综合知识.
而the knowledge of指的是比较具体的某种办法的知识,比如The Knowledge of Life(生活小常识),The Knowledge of Healing(疗愈的知识).