Metaphysics is a broad area of philosophy which has historically ceded ground to science, but which remains very much alive regardless of numerous attempts to finally kill it off. Its purpose must be defined in terms of its territory, which is the conceptual space between two things:
1: Some kind of first principles. This was historically often defined culturally by the prevalent religious environment (such as Hinduism, Buddhism or Christianity). The more purely philosophical option is to define the first principles without reference to religion, as the ancient Greek philosophers did, and as various modern Western philosophers have done. Descartes started with his “Cogito”, Schopenhauer with a blind Will, etc…
2: The best science available. For most of Western history this meant the work of Aristotle’s “natural philosophy”. Aristotle provided his own metaphysics, and the Catholic Church spent over a millenium trying to synthesise Aristotle’s proto-science and cosmology with some rather complicated Christian metaphysical principles. After the scientific revolution this meant classical Newtonian-Maxwellian physics.
Much of the time metaphysics focuses on details – on answering specific questions (such as the nature of free will), or solving specific problems, but the greatest works of metaphysics were grand, systematic attempts to build a bridge between (1) and (2), while answering as many of the important questions and solving all of the most serious problems which needed to answered or solved in order to construct that bridge.
The period between 1900 and 1925 marked a fundamental change in the status of metaphysics. Two things happened together. First, classical physics broke. Einstein’s theories of relativity (1905 and 1915) fundamentally cracked open the idea of a naïve materialistic view of reality, and then in 1925/6 quantum mechanics shattered it entirely. Secondly, Wittgenstein wrote what turned out to be the most influential philosophy book of the 20th century, in which he claimed that metaphysics was necessarily impossible (meaningless), and that we should basically just shut up about it. This was enthusiastically promoted by the logical positivists, and the quantum physicists mostly agreed (“shut up and calculate”).
Metaphysics did not simply roll over and die, of course. But it went into a long decline, and outside philosophy departments nobody took much notice of it for a while. This began to change in the 1970s, partly because the metaphysical questions raised by quantum mechanics had stubbornly refused to go away, and partly because the hippy and new age movements started importing various versions of Eastern philosophy and inventing Westernised versions of them.
However, what almost nobody has even tried to do since then is the grand synthesising task that metaphysics traditionally did: to build a bridge between first principles and known science. Instead what people do is pick some particular metaphysical system, either a whole system from the past, or a partial system from the present day, and try to understand, explain and defend it. This piecemeal approach never gets us anywhere. None of the old systems are any good at the current task, because they were constructed to solve a different set of problems and answer a different set of questions. Firstly we can’t just assume some particular version of Buddhism or Christianity for first principles – not if our metaphysics is intended for consumption beyond that microcosm. It doesn’t necessarily have to be naturalistic, but it needs to be free from religious dogma of any kind. Secondly, those old systems were constructed without knowledge of modern science – especially quantum mechanics, neuroscience/cognitive science, and cosmology. Why am I picking those three? Because each of them is deep in crisis, and the crisis is inescapably metaphysical. The physicalists deny this, of course, but they generally don’t even realise that physicalism is metaphysics itself, let alone being able to understand what is wrong with it. The fact remains that science has made no progress at all on the foundational questions about consciousness – we have overwhelming justification for believing that brains are needed, and we know an awful lot about what brains do, but we can’t answer basic questions about why subjectivity exists at all, or how it relates to the rest of scientific knowledge. How did the first brain evolve if physicalism is incoherent? It is not just the Hard Problem either – there are several other major conceptual problems which reek of metaphysics (the Binding Problem, the Frame Problem, etc..). And in QM’s centenary, we are considerably further away from agreeing on its metaphysical interpretation than we were at the beginning. Any attempt to link these two questions is deeply controversial, because it necessarily highlights the shortcomings of physicalism, and that’s socially unacceptable in science. Additionally, all of the attempts that do exist (Penrose being the perfect example) are themselves problematic. But it is cosmology that is most interesting, because here there are a large number of different anomalies and paradoxes, they are deepening and proliferating, and nobody has got any clear idea of how they are even related to each other, let alone how they might be related to consciousness or quantum foundations.
So there is a massive opportunity here. The situation is screaming the need for a major paradigm shift which spans both science and metaphysics, and the task at hand is the modern version of the task metaphysics always had: to build a grand synthesis which acts a bridge between some kind of first principles (and these must be primarily philosophical rather than religious) and these three different branches of science, all of which are “metaphysically vulnerable”. What is needed is a system which takes the entire problem space into account. It must start with our best science, then closely survey the three big problem areas – then it must try to disentangle the empirical data from the physicalist assumptions which lurk in every shadow. Then it must survey the most important open metaphysical questions (why does anything exist at all? Why does it feel like we have free will? Etc…). And it must then take all of these problems and construct a new grand metaphysical system which succeeds in building a bridge between first principles and empirical data, and in doing so resolves ALL of the major outstanding problems. If it is going to stand up, it needs to make sense of quantum mechanics, cosmology and neuroscience/cognitive science, while also making sense of the fundamental philosophical questions about consciousness, causality, will and the origin of existence.
Very few people are even trying to do this. Nobody in academia is trying to do it, and not many are trying to do it outside of academia either. Instead, most people are still focusing on partial questions, specific problems and tiny details, or trying to defend historical metaphysical systems which were never designed to build the great metaphysical bridge that is needed here and now. Far from being dead, metaphysics is on the verge of a golden age that will eclipse its 18th-19th century heyday.