The research program of New Keynesianism as born in early 1970s was dominated by the search for microeconomic explanations of persistent business fluctuations. For this purpose New Keynesians applied reductionism characteristic of the model of perfect competition. Simultaneously, New Keynesian models reveal different systemic imperfections contradictory to the idea of representative agent. Simple aggregation of (incomparable by assumption) individual results seems to be an obvious paradox. New Keynesian theoretical constructions were divided into three groups: 1. imperfect competition models and heterogeneity of agents, goods and/or transactions; 2. models of heterogeneity between homogenous groups of agents; 3. models of continuum of homogenous agents. Against this background it was shown that reductionism misrepresented the core of Keynesian thought and deprived it of its originality and distinction as compared to the classical approach.