Today, "science" usually refers to a way of pursuing knowledge, not just the knowledge itself. It is mainly about the phenomena of the material world. In the 17th and 18th centuries scientists increasingly sought to formulate knowledge in terms of "laws of nature" such as Newton's laws of motion. And over the course of the 19th century, the word "science" became increasingly associated with the scientific method itself, as a way to study the natural world, including physics, chemistry, geology and biology.