Regarding inventions, the author (1) categorizes into physical-object inventions (e.g. mechanical ones) and material inventions (e.g. chemical ones), focusing on their appearances and properties; and (2) analyzes the formation process of inventions, focusing on the conception based on a principle and the establishment of a model, especially in the case of the invention by experiments, focusing on experimental results (experimental conditions, reproducible phenomena and products having an effect, which appear integrated). The author introduces the idea of "tentative principle" (that is...