The aim of the paper is to advance arguments in favor of the thesis that instrumental rationality is in fact the only form of practical rationality, at work even in those cases in which it seems that human actions are not means to achieve certain ends or to meet certain desires. In this context a crucial role is attributed both to the natural origins and normative aspects of instrumental rationality and means-end reasoning. Particular attention is devoted to the so-called desire-belief model - although subject to significant constraints and additions - which in the analytic action theory has become a nearly universal model of practical rationality in general. The holistic structure of practical reasoning and internalism that this structure involves are finally here considered as both the basic features of human action and the best evidence to support the view that human behavior (including ethical and deontic behavior) is basically instrumental.
Keywords: Desire-belief model, internalism, naturalism, normativity, means-end reasoning, instrumental rationality.