Metaphysics takes it a level deeper

What is metaphysics about? In short, the job of metaphysics is to answer the most fundamental questions about the nature of reality. By "most fundamental" I mean to indicate that I am not talking about the kinds of questions already asked by empirical science, for example about the detectable properties of quasars, neurons or molecules. Those are relatively superficial questions, and easy to answer by just going to a lab and doing a couple of experiments. Metaphysics is about the deep nature of reality.

Here is L. A. Paul on how metaphysics goes deeper than mere empirical science:

"Physics tells us which fundamental (i.e., perfectly natural) physical objects, structures and properties are the actual members of the ontological categories, and metaphysics takes it a level deeper, by telling us what the fundamental categories are, and adding any needed supporting properties and relations (such as identitity, ground, composition, etc.)." (Building the world from its fundamental constituents, 2012; my emphasis)

In physics it is just blindly assumed that there are, say, certain kinds of properties. But in order to know whether there really is such a fundamental ontological category, a category of being, as "property" where mass, charge and so on would belong, we need to do some metaphysics.

As an empirical science, the job of physics is to provide empirically adequate models of observable phenomena. Thus, it stays at the surface level and merely accounts for some superficial features of quarks, photons, etc. It does not tell us what the deep nature of a quark or a photon is, as the metaphysician Meinard Kuhlmann explains:

"the standard picture of elementary particles and mediating force fields is not a satisfactory ontology of the physical world. It is not at all clear what a particle or field even is. ... [Quantum field theory] accounts for our observations in terms of quarks, muons, photons and sundry quantum fields, but it does not tell us what a photon or a quantum field really is." (What is real? 2013; my emphasis)

Therefore, physicists by themselves are not able to give us a complete account of even their own objects of inquiry. If we seek deeper insights into the nature of quarks and fields, it is not enough to learn, by doing some experiments, how they behave. We also need to know what they are, and answering this question is the job of metaphysics, not physics.

Another way to put it is to say that metaphysics provides the very foundation for the nature of reality, as Kit Fine does here:

"[Metaphysics] serves as a foundation, not for reality as such, but for the nature of reality. It provides us with the most basic account, not of things - of how they are - but of the nature of things - of what they are." (What is metaphysics? 2012)