There are some ways in which law can't change and there's some ways in which law must change. So first the way in which law can't change. So both the natural law and positive human law, in some instances, can't change because human nature is relatively static. So a natural law proposition is that human life is good, worthy of pursuit, worthy of preservation. Then that positive law example of that is that it's illegal to take innocent human life. And that so long as human nature doesn't change, and so long as human life is valuable and worth preserving, then that proximate human law derivation against murder isn't going to change. But at the same time the vast, vast majority of positive law is not as closely tied to natural law norms and therefore is not as closely tied to human nature, at least concrete aspects of human nature or the good of human beings. Those other positive law norms may change. In fact, may change with relative frequency, depending on the needs of that community. So you had the common law system that began in England around the 13th century and continues up to today. There have been tremendous changes in the United Kingdom, tremendous changes in the United States since we, in the late 18th century, began our independence under the common law system as well. The common law system has been able to develop, slowly, deliberately, in response to different changes. So for example for those of you who have or are taking property, one of the areas of property that you'll cover is landlord-tenant law. The landlord-tenant law that we in the United States have originated over from the United Kingdom. And originally the landlord-tenant relationship was a feudal relationship, where the landlord would give one right to the tenant. That right was exclusive possession of the feehold estate and that the landlord promised nothing else. That seemed to work decently in the feudal society of early England. But thinking to the United States in the 1970s, the 1980s, there were a lot of cases where state supreme courts, and state courts, faced situations where Americans who were renting property didn't perceive themselves as purchasing only the possession of an apartment. They also wanted to purchase, for example, electricity, water, decent human living conditions. Not having infestations of insects, for example. So the common law system deliberately and thoughtfully changed in response to that new system. And doing so is totally consistent with the natural law because those positive law norms about the relationships between landlords and tenants aren't something that the natural law itself has identified but the natural law has identified that it has to be the case that there should be laws regulating the interactions between people who are landlords and tenants, people who are going to be in a property relationship, so they can maintain their community of justice between the two of them. So that way landlords can't take advantage of tenants and tenants can't take advantage of landlords. The common law system slowly evolved as the needs of different landlords and tenants, in this surrounding society, also changed. So I think that's a concrete example of the ability of the positive law within the natural law tradition to change in response to changed conditions.