This essay, prepared for a symposium on the role of philosophy in law, suggests that philosophical discipline calls into question several features of practical legal decisionmaking. In particular, philosophical analysis of the practice of following rules shows that complying with legal rules when they dictate outcomes contrary to the rule's objectives is irrational. At the same time, important benefits associated with law depend on unreflective application of legal rules, without reference to underlying objectives. Philosophical analysis also suggests that the supposed practice of analogical reasoning in law is illusory. Courts cannot make intelligible decisions based on similarities and differences between cases. At the same time, the process of seeking analogies in the facts and outcomes of prior cases can have salutary effects on judicial rulemaking. This is not to say that philosophers should abstain from analyzing legal practices. Tradition and habit are likely to prevail over philosophical insight in the daily business of judicial decisionmaking.