Last updated: November 3, 2026

Metaphysics is the branch of philosophy that asks what exists and what it is for anything to exist at all. It deals with the questions that sit underneath every other inquiry: whether there is more to the world than matter, what makes a thing the same thing over time, whether properties like redness exist apart from red things, what time and causation really are, whether we act freely, and why there is anything rather than nothing. Physics tells you how the furniture of the universe behaves. Metaphysics asks what counts as furniture.

One clarification first, because half the internet is confused about it. In bookshops and on wellness sites, “metaphysical” has come to mean crystals, auras and manifesting, a usage that goes back to the New Thought movement of the nineteenth century. When a philosopher calls a question metaphysical, she does not mean it is spiritual. She means it is about the basic structure of reality, and usually that it is hard.

Captain Metaphysics and the Charge Sheet

The meme above borrows from the old cartoon Captain Planet. Five young heroes raise their magic rings, and instead of Earth, Fire, Wind, Water and Heart, the rings read “undefined words”, “irrelevant metaphors”, “enormous books”, “obscure vocabulary” and “no proofs ever”. Their powers combine, and out of the sky flies a muscular blue superhero with green hair, labelled METAPHYSICS.

It is a good joke because it is an old accusation in new clothes. David Hume ended his Enquiry Concerning Human Understanding (1748) by imagining himself in a library: any volume of “divinity or school metaphysics” that contains neither mathematics nor reasoning about matters of fact should be committed to the flames, “for it can contain nothing but sophistry and illusion.” In 1932 Rudolf Carnap went further and argued that metaphysical sentences are not even false but meaningless, and that metaphysicians are, in his memorable phrase, musicians without musical ability.

So the meme is right about the charge sheet. Whether it is right about the verdict is another matter, and the most interesting thing about metaphysics is that every attempt to bury it has turned out to contain some metaphysics of its own. But first we should know what the defendant is.

A Name Invented by an Editor

The word “metaphysics” was not coined by a philosopher who wanted to sound profound. Aristotle never used it. When his lecture notes were collected and arranged, probably by Andronicus of Rhodes in the first century BC or by editors working around that time, a bundle of treatises was shelved after the books on nature, the Physics. They became ta meta ta physika, “the things after the physics”. It is roughly as if a branch of knowledge had been named “the box next to the other box”.

Later readers liked to hear “meta” as “beyond”, and the misunderstanding was a happy one, because Aristotle’s own description of the subject is exactly that ambitious. In those books he calls it “first philosophy” and also a kind of wisdom, and he defines it as a science that studies “being as being”: not what it is to be a fish, a planet or a number, but what it is to be at all. The first line of the collection sets the tone for everything that followed: “All men by nature desire to know.”

Aristotle was answering predecessors who had already asked metaphysical questions without the label. Thales thought everything was ultimately water. Parmenides argued that what is not cannot even be thought, and concluded that change and plurality must be illusions. Heraclitus, as later writers reported him, held that everything flows, which is why you cannot step into the same river twice; we have a separate post on what Heraclitus actually said. And Plato answered both with his theory of Forms, in which the changing things we see are copies of unchanging patterns we can only think. Aristotle pulled the Forms back down into things themselves, a quarrel told in Plato vs Aristotle.

What Makes a Question Metaphysical

Students are sometimes asked to devise a metaphysical question of their own. It is a good exercise, and three features give such questions away.

First, they are general in a particular way. “Is there a coffee cup on my desk?” is an ordinary question. “What is it for a cup to exist, and would the cup still exist if the clay had been shaped into a bowl?” is a metaphysical one. It is about kinds of being, objects, properties, events, minds, rather than about which items happen to be around. Second, they often involve necessity and possibility: not just what is the case but what could have been otherwise and what could not. Third, and this is the real test, more observation of the same kind will not settle them, because any observation you make already assumes some answer. A microscope can show you the molecules in the cup. It cannot tell you whether the cup is something over and above those molecules.

That is why “metaphysical thinking”, in the philosopher’s sense, is not a mystical state but a habit of pushing a question one level down. Take any ordinary thing and ask what it is for that thing to be what it is, when it begins and ends, and whether it could have been different. Is a hole something, or just a place where something is missing? (David and Stephanie Lewis wrote a whole paper on that in 1970.) Does a song exist when nobody is singing it? When you fold a sheet of paper into a crane, have you made a new object or merely rearranged an old one? Is a law of nature a rule the universe obeys, or only a summary of what happens to happen? Each of these sounds childish for about ten seconds, and then it does not.

It also helps to separate metaphysics from its neighbour. Epistemology asks how we know; metaphysics asks what there is to be known. “Can I be certain the external world exists?” is epistemology. “If it exists, is it made of matter, of ideas, or of something neutral between them?” is metaphysics.

The Big Metaphysical Questions

Most of the field can be mapped onto a handful of questions that have been argued over for centuries. None of them has a consensus answer, but each has a small set of serious positions, and knowing them is the quickest way into the subject.

A few of these have their own posts here. The fight between matter and mind is the subject of Materialism vs Idealism, Ockham’s suspicion of unnecessary entities is in Occam’s Razor Explained, Hume’s demolition of necessary connection is in why Hume says you cannot infer causation, and Augustine’s famous confession, that he knows what time is as long as nobody asks him, opens Is Time an Illusion?. Rather than skim all eight, it is more instructive to watch one of them work.

Two Ships and One Theseus

Plutarch tells us that the Athenians kept the ship in which Theseus had sailed home from Crete, replacing its planks one by one as they rotted, until philosophers began using it as an example in the argument about things that grow and change: was it still the same ship? Thomas Hobbes, in the seventeenth century, made the puzzle nastier. Suppose someone collected every discarded plank and reassembled them in the original order. Now there are two ships. One has the continuous history; the other has all the original matter. Which is the ship of Theseus?

Notice what kind of question this is. No further fact about wood will help. You can know the position of every plank at every moment and still not know the answer, because what you are missing is not information but a criterion of identity. Hobbes himself concluded that it depends on what the name is taken to track: the matter, the form, or the whole collection of features. That sounds like a shrug, but it is a substantive thesis, namely that identity over time is partly fixed by our concepts rather than read off the world.

The same puzzle becomes urgent when the ship is you. John Locke argued that personal identity consists in consciousness, so that you are the same person as someone in the past if you can remember their experiences from the inside. Thomas Reid answered with his brave officer: a boy is flogged for robbing an orchard, the young officer who takes a standard in battle remembers the flogging, and the old general remembers the battle but not the flogging. By Locke’s criterion the general is the officer and the officer is the boy, but the general is not the boy, which breaks the logic of identity. It is a small story with a sharp point, and it is still taught in every course on the subject.

You will often read that every cell in your body is replaced every seven years. It is a myth: many neurons, and the cells in the core of the eye lens, stay with you for life. The puzzle does not need it anyway, because your memories, character and beliefs change even if your atoms stay put, and the question of what makes the later you still you remains exactly where it was.

Why Is There Something Rather Than Nothing?

If metaphysics has a signature question, it is this one. Gottfried Wilhelm Leibniz put it plainly in 1714: the first question we have a right to ask is why there is something rather than nothing, “for nothing is simpler and easier than something.” His answer was the principle of sufficient reason. Nothing happens without a reason why it is so and not otherwise, so the whole series of contingent things must have its reason in something that exists necessarily, which he called God.

In 1929 Martin Heidegger gave an inaugural lecture in Freiburg with the very title we are trying to answer, What Is Metaphysics?, and he answered it by talking about the nothing. In anxiety, he argued, beings as a whole slip away from us, and in that slipping we encounter the nothing, which is not simply the absence of things. The lecture contains the sentence that made him famous among his enemies: “Das Nichts selbst nichtet”, the nothing itself nothings.

Carnap picked out exactly that sentence as his prize specimen of nonsense. “Nothing” is not the name of a thing, he argued, but a way of saying that there is no thing; to treat it as a subject that does something is a grammatical mistake dressed up as depth. The clash between the two men is one of the founding scenes of the split between analytic and continental philosophy, and a fair judge has to admit that both had a point. Heidegger was trying to describe an experience that ordinary grammar handles badly, and Carnap was right that bad grammar is a poor guide to reality.

The modern versions of the debate are less dramatic but no less stubborn. Bertrand Russell, debating Frederick Copleston on BBC radio in 1948, refused the demand for an ultimate explanation: “I should say that the universe is just there, and that’s all.” Some physicists have offered quantum theory as the answer, most loudly Lawrence Krauss in A Universe from Nothing (2012). The philosopher of physics David Albert replied that a quantum vacuum, with its fields and laws, is a very particular something. We have a whole post on the question, with a meme to match: Why Is There Something Rather Than Nothing?.

The Funeral That Keeps Being Postponed

Metaphysics has attended most of its own funerals. Immanuel Kant began the Critique of Pure Reason (1781) by observing that metaphysics had once been called the queen of all the sciences and was now a battlefield of endless controversies. His remedy was not abolition but a strict border: we can know the necessary structure of experience, space, time, causality, but not things as they are in themselves. The result, explained in Kant’s Thing-in-Itself, is itself one of the most ambitious metaphysical systems ever built.

The logical positivists of the Vienna Circle tried the most radical burial. A sentence is meaningful, they said, only if it can be verified by experience or is true by definition, and metaphysical sentences are neither. The difficulty arrived quickly and never left: the verification principle cannot itself be verified by experience, nor is it true by definition. By its own standard it is metaphysics.

The revival came from within analytic philosophy itself. In “On What There Is” (1948), W. V. O. Quine noted that the ontological problem can be put in three monosyllables, “What is there?”, and answered in a word, “Everything”, after which the real disagreements begin. His criterion, “to be is to be the value of a variable”, meant that you are committed to whatever your best theories need to quantify over, so physics without metaphysics is impossible: a theory that talks about numbers or fields is already taking a stand on what exists. Saul Kripke’s lectures Naming and Necessity (1970) then made necessity respectable again by arguing that some truths, such as that water is H₂O, are necessary even though we discovered them by experiment.

What followed would have delighted the meme. David Lewis defended modal realism, the view that every way the world could have been is a concrete world as real as ours, and he admitted that the main objection to it was not an argument but an “incredulous stare”, which he noted cannot be refuted. On the question of when several things compose one thing, Lewis said always, so that the front half of a trout plus the back half of a turkey make a perfectly good object, the trout-turkey. Peter van Inwagen said almost never: there are simples and there are living organisms, and the table you are reading this on is, strictly speaking, simples arranged tablewise. Both positions are defended with rigorous arguments. Neither comes with a proof that compels the other side. If that is what the meme means by “no proofs ever”, it has a point, though the same is true of most interesting questions outside mathematics.

What Physics Cannot Settle on Its Own

The commonest objection to metaphysics today is that science has taken over its questions. Some of them it has: nobody now asks philosophers what the elements are. But look at the questions physics hands back.

Quantum mechanics is the most precisely confirmed theory we have, and physicists still disagree about what it says the world is like. On one interpretation the wave function collapses when a measurement occurs; on another it never collapses and the universe branches into many worlds; on a third particles always have positions and are guided by a wave. Most of these make the same predictions for every experiment performed so far. Choosing between them is therefore a question about what exists, measurement, branching worlds, hidden positions, given the same evidence. That is a metaphysical question, asked by physicists.

The mind supplies a second example. Neuroscience can tell you which brain processes go with seeing red. Thomas Nagel argued in 1974 that even a complete physical account of a bat would leave out what it is like to be a bat, and David Chalmers later called the question of why physical processing is accompanied by experience at all “the hard problem of consciousness”. Whether the hard problem shows that the mind is more than matter, or only that our concepts of mind and matter are poorly fitted to each other, is again not something a brain scan will settle. If you want the zombie version of the argument, read A Thriller and a Thought Experiment.

And sometimes the question arrives in technological costume. Nick Bostrom’s simulation argument (2003) reasons from computing power to the conclusion that either civilisations almost never reach the stage of simulating their ancestors, or they almost never choose to, or we are very probably living in such a simulation. It is a metaphysical argument that happens to mention graphics cards, and a cousin of Last Thursdayism.

Metaphysics at Three in the Morning

Back to Captain Planet. Of the five rings, the meme gets two roughly right: the books are enormous and the vocabulary is obscure. But the other three accusations are closer to the opposite of the truth. Metaphysicians are, if anything, obsessed with definitions, which is why their papers are so long, and they distrust metaphors so much that they spend whole careers removing them. As for proofs, metaphysics has the same kind of rigour as the rest of philosophy: it cannot force agreement, but it can show exactly what each answer costs, and that is no small thing.

It also matters more often than it seems. Whether a corporation is a person, when a human life begins and ends, whether an AI system could be conscious, whether you are responsible for what you were determined to do: these are not merely legal or scientific disputes. Each one rests on a metaphysical view about identity, minds or freedom, and people who say they have no metaphysics usually just have an unexamined one.

Bertrand Russell, who had little patience for grand systems, still ended The Problems of Philosophy (1912) by defending the questions themselves. Philosophy, he wrote, is to be studied not for any definite answers, “since no definite answers can, as a rule, be known to be true,” but because its questions “enlarge our conception of what is possible” and “diminish the dogmatic assurance which closes the mind against speculation.” That is as good a description of metaphysics as you will find. So the next time you lie awake wondering whether you are the same person who went to bed, whether the past is still real, or why there is anything at all, you are not having a crisis. You are doing what Aristotle said all people do by nature, and you are in excellent company.