We explore some logics of change, focusing on commands to change the world in such a way that certain elementary propositions become true or false. This investigation starts out from the following two simplifying assumptions: (1) the world is a collection of facts (Wittgenstein), and (2), the world can be changed by changing elementary facts (Marx). These assumptions allow us to study the logic...

Few students of the subject of intoxicants and traffic safety now doubt that marijuana, like alcohol, can exert detrimental influence. Just how detrimental is debatable. The debate pits optimists ("it's much less of a problem than alcohol") versus those on the pessimistic side ("but who needs any new problems?"). Yet there can be no question that some drivers who met their ends on the highway w...