Law is a complex subject that has been the object of study for millennia and continues to be a source of scholarly inquiry into such fields as legal history, philosophy, economic analysis and sociology. At its core, law is concerned with the principles and practices that govern people’s interaction with one another and how they can be held accountable by their government and peers.
Law serves many goals but the four principal ones are establishing standards, maintaining order, resolving disputes and protecting liberties and rights. Laws must be fair and equitable, meaning that they should not discriminate between people based on their social status or wealth. They must be public, meaning that they are open and accessible to all, and they must be clear, so that non-experts can understand them.
From a methodological point of view, law has some peculiar features that make it different from empirical science (like the laws of gravity) or even social science (like the law of demand and supply). In particular, it is normative. Laws tell people how they ought to behave or what they must or must not do. But such normative statements are deprived of the same level of evidence that would be required to support them in other fields.
Furthermore, the nature of the physical world and the limitations inherent in human capabilities make it impossible to require that people do things that are beyond their capabilities. For these reasons, there is a long tradition of opposition to the idea of Bills of Attainder.