Abstract: Personal knowledge differentiates narrating and memory knowledge and Polany attaches great significance to the comprehension elements of these two knowledge.The two kinds of knowledge are in accordance with prescriptive and retrospective judgments,with these two judgments following no rules,resting on comprehension and in accordance with scientific comprehension and explanation.Scientific explanation is the system for narrating knowledge and comprehension is the explicating system for memory knowledge,with their common purpose of solving the problems of commonness and specifics.