Justifying Metaphysics to its Critics

There has been a (to me gratifying) rebirth of metaphysics in English-speaking philosophy over the last couple of decades. Now, just as in the past, there is a backlash coming from within the profession. One locus of the opposition comes from philosophers of science. Now one of the best contemporary philosophers of science, Craig Callender, has a draft paper (“Philosophy of Science and Metaphysics”) giving his own critical assessment of metaphysics, which he presents in a judicious and thoughtful manner. (For a recent bloggy example of the tension here, see the sometimes pointed debate down in the comments to this post at It’s Only A Theory.)

Callender believes metaphysics plays an important role in science itself as well as philosophy of science. But he thinks some metaphysics goes wrong by assuming too much autonomy from science: there is a “resurgent idea that metaphysicians have a wider domain of study than scientists.”  As a result:

Today metaphysics is again the target of deep suspicion. In fact, we are in the midst of a flare-up of historic proportions. Evidence of this comes from my bookshelf. Many recent books in philosophy of science possess entire chapters strongly condemning comtemportary analytic metaphysics.

To explore why this has come about, he presents a brief sketch of post WW-II philosophy: first, Quine’s critique of positivism took away one reason to reject metaphysics; second, exploration of modal logic and counterfactuals in the 1960’s and 70’s made modality a respectable part of the subject; and third Kripke’s work convinced others we could use our intuition to describe and analyze metaphysical modality.

Subsequently, Callender says, some philosophers began to embrace the idea that while science explores the actual, metaphysicians are empowered to explore not only the actual but the metaphysically possible. And the only equipment needed for this was an armchair.

At the same time, while Quine helped “clear the room” for metaphysics (while Kripke “furnished it”), Quine was clearly no friend of metaphysics and helped bequeath a strong naturalistic bent to philosophy which gave primacy to science and suggested philosophy had a supportive, not groundbreaking, role to play in advancing our knowledge (whence the critics).

As Callender goes on to further diagnose, what clearly bothers critics about modal metaphysics is this idea that it is an exclusive philosopher’s playground (to David Lewis, “a philosopher’s paradise”). How can this idea be justified? Here’s the heart of the matter:

Where do we acquire the ‘modal intuitions’ that are the currency of the field? How do we know that they’re reliable? What are they of? Shouldn’t intuitions of what is possible make some contact with science? [emphasis original]

In the next section of the paper, Callender picks on some examples of recent metaphysical discussions which seem shallow or pointless to critics (some mereology). But he concedes one needs some sound criteria from which to try to distinguish the good from the bad metaphysics.

His prescription is to do away with the idea that metaphysics can be completely independent of science. What is deemed possible and necessary needs to come from a scientific theory, allowing that it can be a new and unproven theory. (The metaphysican would respond that this would only give you a species of what’s physically or nomologically possible). In other worlds, Callender says you need to construct the space of possibilities with a good theory which is based on explaining the actual, not just rely on our conceptual apparatus to somehow be putting us in touch with a space of metaphysical possibilities.

Again, the suspicions about metaphysics are traced to the question of how we know our modal intuitions are reliable. Modality needs to be grounded in something more tangible.

In his concluding chapter, Callender wants to emphasize that despite his negative arguments, he thinks metaphysics has an important role to play, and needn’t only follow where science leads. Metaphysics can help explore future directions as well as deepen understanding of existing models.

My take (because this topic clearly needs input from an outside amateur!): I think modal metaphysics is can meet the challenge posed by critics. There is a good reason to think that our modal intuitions are sound.

First an observation: when you look at the work of theoretical physicists themselves these days, the notion of what might be physically possible in cutting edge theories seems to me to be converging quickly to the metaphysician’s broad view of what’s possible - essentially that it maps to what is logically possible. Hugely expansive multiverses are being proposed again and again with a variety of motivations. (Off the top of my head: explaining the fine-tuning of physical constants or the low entropy big bang, the many-worlds interpretation of quantum physics, eternal inflation bubbles, the string theory landscape, loop quantum cosmology “big bounces”; by the way it appears Craig Callender is skeptical of multiverse proposals based on this review of Sean M. Carroll’s new book).

But here’s my thought. A metaphysical picture which is naturally motivated by quantum physics (science!) gives us at least a good sketch of why our modal intuitions should be reliable. Our world consists of a causal series or network of quantum measurement events. Each event is a “collapse” of a number of possibilities into a single actuality. While we don’t understand the details yet of how our brain/body system works, we can infer that our participation in this network acquaints us with natural possibility at the ground level. This helps explain, by the way, why assessing possibilities is central to our practical lives (as it is to even the most primitive living things).  Experience with these natural possibilities throughout our evolution should be expected to give rise to a reliable conceptual faculty for extrapolating our experience via modal reasoning.