One of the works that a professional ethicist should do in the field of applied ethics is to explain some concepts commonly used in other sciences. This paper considers the concept of "influence" from such a viewpoint. first, we prescribe the meaning of "influence" and the use of it, and then, clarify the difference between two explanations of influence. The whole consists of 6 chapters: 1) preface, 2) the concept of "influence", 3) the causal explanation of influence, 4) a sample of train accidents, 5) the subjective explanation of influence, 6) in closing.

The word of "influence" is used variously, such, for example, as "influences on the body and health", "influences on natural surroundings", "influences of the internet and game software upon children's spiritual growth", etc. "Influence" is defined as "bringing the change to something by acting on it". It can be used both in the plus direction and the minus direction. There seems to be a causal relation between A and B in the proposition "A has an influence on B". An influential relation which is often compared to the causality exhibits an ascendant causality deduced from the effect. This is called "the causal explanation of influence". We consider the point at issue concretely, as giving such a case as the train accidents. This explanation presupposes that something happens when it ought to happen. However, it is insufficient to understand an influential phenomenon more widely. If we take up what happens in the correlation with what doesn't happen, "influence" can be grasped as "the change" of the latter into the former. What does this mean? Paying attention to the change will lead to the discovery of "the subject free from influence". Therefore, an influential relationship is to define with a description that something can have an influence because there is the subject influenced. This is called "the subjective explanation of influence". Thus, this paper points out that the fault of the causal explanation should be supplemented with the subjective explanation.