Analogy plays a basic part in engineering which is subject to certain limitations, due to the following reasons:— lack of accuracy of the measuring instruments and of computing data; — simplifying assumptions necessary for establishing the mathematic model; — restrictions due to compulsory computation means and time. The basic criterion of engineering knowledge is efficiency. The engineer works thus on successive approximations, each of them corresponding to a more or less appropriate model of the final result. In order to avoid (...) disappointment, it is very important for him to be conscious of the relativity of his knowledge and of the scope of teh successive approximations. This procedure is the same for other fields of knowledge and provides an opportunity to specify the concept of rigour applying to each. It shows the practical, limited and revisable character of any knowledge not springing from metaphysics. (shrink)

RÉSUMÉDifférentes méthodes ?identification des systèmes ont été développées par les informaticiens qui consistent à déterminer à partir de ľobservation des grandeurs ?entrée et de sortie de ce système, les relations de cause à effet qu'il établit entre ces grandeurs.Cet exposé rappelle le principe des méthodes ?identification 〈statique〉 et 〈dyna‐mique〉, et conclut que ces méthodes peuvent être considéréd comme un exemple ?applications des approches définies par la philosophic de ľouverture pour ľacqui‐sition de nouvelles connaissances.