The views of M. Mandelbaum on the historiography of philosophy have undergone a certain evolution. The paper shows the epistemological foundations of Mandelbaum’s historical and philosophical position. From the standpoint of critical realism and its application to social sciences Mandelbaum shows the advantages and disadvantages of the monistic or holistic approaches, partial monisms and pluralism. He considers A. O. Lovejoy's history of ideas to be the most reasonable pluralistic conception, although its use as a historical and philosophical methodology is limited. Intellectual history, which replaced it, should be called a partial monism, however, according to Mandelbaum, it gets a number of advantages if it begins to use a pluralistic methodology. In this version of methodology, the history of philosophy and intellectual history can be identified. The paper also presents some objections of analytic philosophers against this identification.