 In reply, van Fraassen (2001) suggests that what we see through a microscope is akin to reflections seen in mirrors and other reflective surfaces—the reflection of a tree in a body of water, for instance. In both the case of the observation via the microscope and the object viewed in a reflection, we might assert that what we are seeing is a real object. But van Fraassen points out an important difference between the reflected object and our observation through the microscope. We are confident that the reflection is of a real object because we can observe certain invariances between the object purportedly being observed (the tree), the reflective image, and our vantage point. We can, for instance, see that the tree maintains a certain fixed position relative to the reflective body, and we can see that the angle subtended by the lines between us and the two bodies is a particular function of the observer’s position. The observation of these invariances is possible, in part, because the tree is itself observable without the aid of instruments (van Fraassen 2001, 160).