ABSTRACT
The logical empiricists early identified several features of a law on which there has continued to be wide agreement: laws are universal statements of the form “All a’s are b’s,” or “Whenever an event of type C occurs, an event of type E occurs,” or again, “If (an) event e happens, then invariably, (an) event f occurs.” For example, “All pure samples of iron are conductors of electric currents at standard temperature and pressure,” or “Whenever an electric current is applied to a sample of iron under conditions of standard temperature and pressure, the iron conducts the current,” or “If an electric current is applied to a sample of iron under standard temperature and pressure, then the sample conducts the current.” These are terminological variants of the same law. Philosophers tend to prefer the “if ... , then ... ” conditional version to express the form of a law, leaving the universality of the law implicitly understood. But being a statement of universal form is obviously not sufficient for being a law: consider; “All bachelors are unmarried,” and “All even numbers are divisible without remainder by 2.” Neither of these universal statements are laws, even though both have the same logical form as laws. They are not laws evidently because they are true by definition, whereas laws are made true by facts about the world.
