Abstract
We have to judge the condition of the environment around us to keep our life from danger. The environment is such abstract conception that we cannot observe it directly to judge its codition. We need observe several phenomena happening around us to estimate the condition. Indexes of environment are tools to grasp the phenomena and to discribe their conditions. The contents of indexes are regarded as messages from the environment to observers. They try to receive as many messages as possible to judge the condition more correctly. The degree of contribution to correctness is amount of information carried by the message. Important indexes are those which send messages conveying large amount of informa tion to the observer.
This paper stands on recognition above to aim at analysing the role of indexes in discrimination of environment.
