" Twentieth-century empiricism made an important mistake here. We can make sense of science only by treating much of it as an attempt to describe hidden structures that give rise to observable phenomena. This is a version of scientific realism, an idea that will be discussed later in this book. In science there are depths. There is not a simple and fixed distinction between two "layers" in nature-the empiricists were right to distrust this idea. Instead there are many layers, or rather a continuum between structures that are more accessible to us and structures that are less accessible. Genes are hidden from us in some ways, but not as hidden as electrons, which in turn are not as hidden as quarks. Although there are "depths" in science, what is deep at one time can come to the surface at later times, and there may be lots of ways of interacting with what is presently deep. "

― Peter Godfrey-Smith , Theory and Reality: An Introduction to the Philosophy of Science