And yet, every method physicists and chemists have devised for looking at matter says that it is. And scientists are in the business of formulating much more systematic posits, based on kinds of experience we normally don't encounter. Yes, scientific laws are posits, which means that we are not certain that they are true. Contrary to the words of many, good theories don't grow up to be laws. They are quite different in nature and purpose.
Scientific laws are descriptions of the ways that matter and energy behave.
Laws are often expressed best mathematically, since they represent observed patterns of behavior. For example, in the early days of modern chemisty, scientists observed the ways in which different elements combined with each other. But they were able to observe some very consistent behaviors. For instance, hydrogen and nitrogen will combine together to form ammonia. And when hydrogen combines with oxygen to form water, it always takes twice as much hydrogen as oxygen.