I think that metaphysics is the most important issue in philosophy. The problem is that, since it is closely connected with ontology, it can be interpreted and reconsidered in so many ways that it can become just a point of confusion.
The word means literally "beyond physics". This expression can be considered from two essential perspectives.
One is that adopted by, for example, some artists, where "beyond physics" means beyond the world of material things; so, these artists try to represent pure emotions, feelings, abstract ideas. This is not the perspective we are interested in here.
The other perspective is that stemming from Aristotle, since his books describing the nature of things were called "metaphysics" because they were physically beyond, which means after, his books about physics. This important coincidence is the origin of the philosophical meaning of metaphysics. The basic meaning of "metaphysics" in philosophy thus depends on how we interpret the meaning and the importance of Aristotle's research. Since different philosophers have interpreted differently the other philosophies, as a result we have not a final, exact meaning of "metaphysics". However, I think that, at this point, we can ask what the best, the most productive, the most fruitful, the most useful, definition of metaphysics is. I think that this way we can obtain good results.
I think we can say that ontology is about being, while metaphysics is about how things are. This implies a specific interpretation of Aristotle's research. In this perspective, we interpret Aristotle's research as an effort to compensate the unreliability of knowledge acquired through physics. Knowledge acquired through physics is unrealiable because it relies on our senses: sight, hearing, smelling, touching and so on. Everyone can see that our senses can be easily deceived: we see an animal and after approaching it we realize that actually it was just a stone, or a plant. We interpret that Aristotle found a solution to this problem in the use of reason: reasoning, applied to the data given by our senses, is able to compensate and solve the problem of unreliability of senses. So, he elaborated all the stuff we know about form, substance, nature, essence and so on. What is important is that this way his highly systematic work gave a very strong and reassuring impression of order, domain over reality, reliable knowledge. Many philosophers after, or even before Aristotle, can be interpreted this way: they tried to find some strong interpretation able to explain how things are.
Now we can realize some points that are very useful to clarify what metaphysics is or implies. Metaphysics means:
- having been able to finally reach truth, true knowledge, absolute and objective certainty;
- that reality exists out there, it is not a dream, an illusion produced by our mind.
All of these strong points are based on the irresistible strength of logic, reasoning, whose roots are in Parmenides' principle of non contradiction. As a consequence, those who disagree must necessary be people who either don't understand, don't know, or are mad. Logic and reasoning are the roots of truth and, as such, the roots of what is good. From here, a lot of theology can be built, based on metaphysics.
Now we can better realize the difference between metaphysics and ontology: metaphysics is about the truth of being, the absolute certainty of reality; since ontology is just about being, if, for some reason, we say that "being" means actually doubt, or involvement in human time (Heidegger), or subjectivity, in that case what we say is ontology, because it is about being, but is not metaphysics, because it disagrees with the concept of objective truth, objective reality.
It is good to realize that, even when we say that the world is just a dream produced by our mind, although apparently this can be considered something non metaphysical, since it is against the idea of objective reality, actually it can still be accused of being metaphysics, because its conclusion sounds like "the real, objective, absolute truth, is that the world is a dream". Similarly, when we say that "everything is relative", this can be accused as well of being just another metaphysics, because it tries again to reach a final conclusion about "how things really are".
At this point the question is: is it possible to make a truly non-metaphisical philosophy, since, whatever we say is exposed to the criticism of being just another attempt of finally establishing how things objectively are?
One way to try to exit this cage is trying to be aware of the constraint coming from language: language is made grammatically in a way that forces us to talk by assertions, statements, that again and again make us fall into the mechanism of saying how things are. So, we can try some workarounds by specifying that what we say is not meant to be a final, objective, metaphysical statement.
Another way is to make clear that what we say is meant to be a subjective opinion, an hypothesis, an attempt. In this context, the opposite of metaphysics is the subjective perspective. Another philosophical perspective that is one of the greatest efforts to be non-metaphysic is postmodernism. There is also the "weak-thought" of the philosopher Gianni Vattimo.