Philosophy likes to see itself as on the hunt for eternal truths, from moral facts to the deep structure of reality. But this story mistakes what metaphysical language does, argues Amie Thomasson, whose recent book Rethinking Metaphysics has caused a stir in this most ancient of disciplines. Recent work in linguistics—largely overlooked by philosophers—shows that classic metaphysical concepts arise not to describe reality but as tools for getting things done. Metaphysics isn’t about describing reality, but rather redesigning and engineering language to sharpen its tools, to enable us to do new, better things with it.

Metaphysics has been going on for a long time. It’s high time we rethink it. Those who do metaphysics ask questions about what exists, and about the natures of things, their “essences,” and whether they are fundamental or “grounded” in other things.

While metaphysics reaches back in the Western tradition at least to ancient Greece, you might understandably ask: These days, aren’t those questions addressed by the sciences? We look to biology to determine what kinds of life there are, to physics to find out if there are supernovas, to chemistry to find out what the fundamental elements are, etc.

A common reply is to say: Sure, science answers some of these questions, and where it does, metaphysics should work hand in hand with the sciences. But metaphysics (they say) is broader, concerned with “everything whatsoever.” So, metaphysics also asks questions like: are there (or are there really) numbers, properties, moral obligations, possibilities or even possible worlds? Are moral properties grounded in natural properties? And so on.

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I begin from the simple point that we shouldn’t just assume that all parts of our language function in the same way.

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In Rethinking Metaphysics, I ask: What if some of these words (“number,” “property,” “possibility,” “moral obligation”…) aren’t even trying to pick out some parts of the world that we can just look for, identify, and study as we can study plants, animals, or supernovas? What if these words play a very different role in our language? Assuming that they just “pick out” (or perhaps try and fail to pick out) features of our world, which we can go on to investigate, relies on assuming that all these nouns work in the same way: that they aim to refer to and describe some features of the world. This is to make what I call the “functional monist” assumption. All the recent major approaches to metaphysics make this assumption, and it leads them astray.

Metaphysicians often reply: “Functional monism is a thesis about language. But I’m not interested in words, I’m interested in the world. So, I don’t care about how our terms such as ‘possibility’ or ‘redness’ or ‘the number seven’ or ‘moral obligation’ work. I’m interested in whether there are such things, and if so, what their natures or essences are, whether they are fundamental, or what they are grounded in.”

But if these terms enter language in a different way, and function differently than our terms for observable, concrete parts of our environment—if they aren’t even attempting to pick out features of the environment—then asking questions like these may be a mistake. In Rethinking Metaphysics I begin from the simple point that we shouldn’t just assume that all parts of our language function in the same way. Before we launch into “metaphysical investigations,” we should first ask what functions these terms serve, and how they enter language.