Abstract

Biologists are not used to the term „substance". They prefer to say „a living being", „an organism", a „specimen of species Homo sapiens'' - for instance. Chemists, on the other hand, when they say „this is a new substance" they usually mean the same Aristotle would mean - I think. The chemical meaning of the term „substance" is closest to the one I am going to discuss in this paper. To know a substance, one has to accumulate and store a multitude of different forms of evidence concerning this „natural behavior". So that concept of the „nature" of a given chemical substance is necessarily very complex and it cannot result from a single sensation, or a momentary observation