This article is an attempt to examine the concept of obligation in Kantian ethic from three viewpoints of semantics, epistemology and ontology. On the basis of semantics, obligation is an act one is required to do. Requirement, then , is the a necessity of a free act under the rule of reason. Epistemologically speaking, reason is the source of ethical rules and obligations. Morel rules are a priori synthetic ones and categorical imperative is that by which one can recognize his own moral duties. Reason as Kant believed not lays down but discovers moral rules. Ontologically Kant held ethical realism. He lists different kinds of duties. In his view the categorical moral rules are not conditioned to any end and thus not susceptible of any exception. There is no possibility of conflict among the moral obligations. Ethical theory of Kant is based on different epistemological, humanological, and axiological assumptions.
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