The casuality problem in atomic physics is analysed by Bohr in a wide methodological context. The first part of the paper is a short historical essay picturing the entry of statistical concepts into physics. Bohr underlines a close relationship between an unavoidably probabilitic nature of the quantum theory and quantum postulates introducing the alien-to-classical-physics concepts of integrity, individuality of atomic processes. In the second central part of the paper Bohr discusses the casuality problems in atomic physics in detail and shows that their solution requires a careful analysis of the observation process. Proceeding from the program methodological requirement to describe the measuring instrumentation operation and observation results in the language of classical physics, he explains that the statistical character of the uncertainty relationships expresses a substantial specifically quantum constraint to the applicifically of classical conceptions analyses of microphenomena. Then Bohr refines in principle the notion ''phenomenon'', as one of the central notions among those he employed for the formulation of his complementarity principle. According to bohr a phenomenon should be under-stood as an unambiguously present situation of a completed experiment. Therefore, it is erroneous to speak of the phenomenon perturbation by the observation. The final part of the article deals with the discussion of methodological parallels of the quantum theory and relativity theory.