What is Metaphysics?:
In Western philosophy, metaphysics has become the study of the fundamental nature of all reality what is it, why is it, and how are we can understand it. Some treat metaphysics as the study of higher reality or the invisible nature behind everything, but that isnt true. It is, instead, the study of all of reality, visible and invisible; and what constitutes reality, natural and supernatural. Because most of the debates between atheists and theists involve disagreements over the nature of reality and the existence of anything supernatural, the debates are often disagreements over metaphysics.
Where does the Term Metaphysics Come From?:
The term metaphysics is derived from the Greek Ta Meta ta Physkia which means the books after the books on nature. When a librarian was cataloging Aristotles works, he did not have a title for the material he wanted to shelve after the material called nature (Physkia) so he called it after nature. Originally, this wasnt even a subject at all it was a collection of notes on different topics, but specifically topics removed from normal sense perception and empirical observation.
Metaphysics and the Supernatural:
In popular parlance, metaphysics has become the label for the study of things which transcend the natural world that is, things which supposedly exist separately from nature and which have a more intrinsic reality than our natural existence. This assigns a sense to the Greek prefix meta which it did not originally have, but words do change over time. As a result, the popular sense of metaphysics has been the study of any question about reality which cannot be answered by scientific observation and experimentation. For atheists, this sense of metaphysics is usually regarded as literally empty.
What is a Metaphysician?:
A metaphysician is someone seeking to understand the substance of reality: why things exist at all and what it means to exist in the first place. Much of philosophy is an exercise in some form of metaphysics and we all have a metaphysical perspective because we all have some opinion about the nature of reality. Because everything in metaphysics is more controversial than other topics, there isnt agreement among metaphysicians about what it is they are doing and what they are investigating.
Why Should Atheists Care About Metaphysics?:
Because atheists typically dismiss the existence of the supernatural, they may dismiss metaphysics as the pointless study of nothing. Because metaphysics is technically the study of all reality, and thus whether there is any supernatural element to it at all, in truth metaphysics is probably the most fundamental subject which irreligious atheists should focus on. Our ability to understand what reality is, what it is composed of, what "existence" means, etc., is fundamental to most of the disagreements between irreligious atheists and religious theists.
Is Metaphysics Pointless?:
Some irreligious atheists, like logical positivists, have argued that the agenda of metaphysics is largely pointless and cant accomplish anything. According to them, metaphysical statements cannot be either true or false as a result, they dont really carry any meaning and shouldnt be given any serious consideration. There is some justification to this position, but it is unlikely to convince or impress religious theists for whom metaphysical claims constitute some of the most important parts of their lives. Thus the ability to address and critique such claims can be important.
What is an Atheist Metaphysics?:
The only thing all atheists have in common is disbelief in gods, so the only thing all atheist metaphysics will have in common is that reality doesn't include any gods and isn't divinely created. Despite that, most atheists in the West tend to adopt a materialistic perspective on reality. This means that they regard the nature of our reality and the universe as consisting of matter and energy. Everything is natural; nothing is supernatural. There are no supernatural beings, realms, or planes of existence. All cause and effect proceeds via natural laws.
Questions Asked in Metaphysics:
What is out there?
What is reality?
Does Free Will exist?
Is there such a process as cause and effect?
Do abstract concepts (like numbers) really exist?
Important Texts on Metaphysics:
Metaphysics, by Aristotle.
Ethics, by Baruch Spinoza.
Branches of Metaphysics:
Aristotles book on metaphysics was divided into three sections: ontology, theology, and universal science. Because of this, those are the three traditional branches of metaphysical inquiry.
Ontology is the branch of philosophy which deals with the study of the nature of reality: what is it, how many realities are there, what are its properties, etc. The word is derived from the Greek terms on, which means reality and logos, which means study of. Atheists generally believe that there is a single reality which is material and natural in nature.
Theology, of course, is the study of gods does a god exist, what a god is, what a god wants, etc. Every religion has its own theology because its study of gods, if it includes any gods, will proceed from specific doctrines and traditions which vary from one religion to the next. Since atheists don't accept the existence of any gods, they don't accept that theology is the study of anything real. At most, it might be the study of what people think is real and atheist involvement in theology proceeds more from the perspective of a critical outsider rather than an involved member.
The branch of universal science is a bit harder to understand, but it involves the search for first principles things like the origin of the universe, fundamental laws of logic and reasoning, etc. For theists, the answer to this is almost always "god" and, moreover, they tend to argue that there can be no other possible answer. Some even go far as to argue that the existence of things like logic and the universe constitute evidence of the existence of their god.