The author singles out various conceptions of rationality used in practical legal discourse: formal and substantive rationality, instrumental goal‐ and means‐rationality, communicative rationality. Practical rationality is expressed in decisions justified by epistemic and axiological premises according to the rules of justificatory reasoning. Five levels of analysis of this justification are identified. Rules, principles and evaluations are used as justifying arguments and their characteristics determine the dimensions of rationality of decision depending on the features of rules, various conceptions of principles, and (...) kinds of relativisation of evaluations. The dimensions of legal rationality depend mainly on three singled out conceptions of rationality, i.e., formal rationality dealing with the deep structure of justification, instrumentally oriented rationality as content of justifiability, and communicative rationality linked with the pragmatics of human interaction. Legitimacy, according to the presented analysis, appears as a subclass of external justification dealing with axiological premisses in terms of instrumental rationality and/or communicative rationality. (shrink)