What does the law demand when it requirescitizens to conform to standards ofreasonableness? I propose and defend theview that the law should demand thatcitizens conform their behavior to someactual conduct in society. I contrast thisidea against what might be called the``empty vessel'' view of reasonableness,where the standard is understood tofunction like an empty vessel in the law,allowing courts to use various norms andmoral judgments to determine what seemsreasonable in the circumstances. Theempty vessel account is the more commonapproach for understanding reasonableness,but (...) it leaves obscure whether and howassessments about appropriate conductconnect with facts about citizens' actualconduct. I argue for a ``binocular'' viewthat focuses our attention on actualpractices and thereby establishes howthese standards provide a stable guide toconduct and support the rule of law. (shrink)