This paper presents general systems theory on the basis of ontology. In this systems theory, systems are epistemic frameworks from a nominalistic point of view, and systems objects are positioned through the systems corresponding to their objects. It is not until the correspondence between a system and its systems object that the reality comes into existence. Systems have to be transformed in conformity with changes in objects' environments. This is in cybernetic processes. Norbert Wiener developed the thought that rigidity must be rejected, so his line of thought is the same as the author's. Thus, postmodern sciences start from ontological commitment and rejection of rigidity.