This article is the introductory research of the meaning and philosophical foundation of "integrative research" in various fields. And the integrative study of social and natural science has been discussed. There are two kinds of integrative studies. One is the integration of fields whose disciplinary domains are ontologically overlapped between each other and the other is integration between disciplinary fields in which there is no ontological overlap. The model of integration is proposed in the case of integrative researches among the areas which have ontologically overlapped among one another. The motivation of integrative research between disciplines is the pursue of completeness of disciplinary field. The meaning of completeness is explained interms of EPR arguments. The concept of disciplinary categories are proposed analogous to Kant's category to understand the complex reality projected in each disciplinary perspective. And through the collection of the grasped contents in each disciplinary category, reality can be recognized. These disciplinary categories are contingent and construed through the practices and cooperations in contrast with Kant's categories. The completeness of ontology of each discipline and the possibility of convergence of disciplines are discussed. And I argue that social science and natural science are different but have similarity in view of causality. The concept of cause is not Humean concept but non-Humean concept as core concept. We illustrate the cases of producing new area through integrative research of natural and social sciences.