Broadly speaking, geology is often divided into major categories: physical geology, which examines Earth materials and seeks to understand the many processes that operate on our planet, and historical geology, which seeks an understanding of the origin of the Earth and its development though time. The science of geology (and scientific inquiry in general) assumes that the world is comprehensible (that is, humans can perceive and make some sense of the world around us) and consistent (that is, although given freedom, it operates with regularity according to natural laws).