Of or pertaining to (the use of) reasoning and logic; thinking or behaving reasonably or logically;

arriving at sound conclusions on the basis of relevant evidence;

rationally directing or changing one’s behaviour involves doing so in such a way as to increase the chances of reaching one’s goals, relative to the information available at the time a decision is taken – on the assumption that such goals are not self-defeating, destructive, or harmful (see: ethics) – rational choices are ones which are in the best interests of the actor taking the decisions, and actions rational to the extent to which they provide a likely and acceptable means to an actor’s (ethical) ends, rational beliefs are beliefs which are likely to be true, cognitive processes are rational insofar as they are reliable; rational inferences or arguments comply with the principles of logic, and so on.