In his book Elbow Room, philosopher Daniel Dennett gently tries to introduce the reader to the idea that there may be no free will. (Dennett supports a version of free will, but one that has major concessions to determinism.) At one point he wants to argue that NOT having free will isn’t what you might think. And here he introduces the idea of the Evil Puppetmaster (my term).

It’s an evocative image. Some kind of evil being in the sky, with a string attached to each of your limbs, deciding everything about what you do. But with no control of your thoughts, so you are stuck there, helpless, moving around the world at the whims of the Evil Puppetmaster, despite your best intentions to do otherwise.

Of course it’s ridiculous, and Dennett uses that fact to help readers understand the terrain better. He wants to reassure us: Don’t worry, no matter what the neuroscientists and the philosophers conclude, there is no chance you will end up as a puppet on a string.

But there are some people who live like this. There are diseases that make you move in ways that are directly opposite to your desires. I want to argue that these are diseases of the free will system. Some of these diseases are, like Essential Tremor, are philosophically straightforward. But some are more complex. And understanding these diseases can, I think, help us understand what free will is.

Tourette Syndrome is usually associated in popular culture with loud cursing, but this is misleading. The most common symptoms are small repetitive movements known as tics, some of them small enough they are more accurately called twitches, but others are full limb or body movements. The disease is not psychosomatic; it’s associated with neuron misfiring in a brain region called the striatum (among other areas), and is (somewhat) treatable with a class of drugs known as neuroleptics.

These movements are not involuntary. They arise as a consequence of intense urges—urges that come out of nowhere and are nearly impossible to resist.

Our actions are typically classified into ‘voluntary’ and ‘involuntary’, but researchers who study Tourette Syndrome have been forced to invent a new word, and it’s one that I love. That word is ‘dysvoluntary’, and it means you can control the action, but it’s incredibly difficult to do so. The fact that scientists are inventing a new word is a sign that something funny is going on. Tourette Syndrome affects your free will system. It doesn’t move your arm involuntarily, it gives you an involuntary urge, an urge that you don’t want.

Tourette Syndrome is a reminder that our desires and our actions don’t have a one-to-one correspondence. They are not the same thing. And when they misalign, it can be very unpleasant. Tourette Syndrome is a reminder that we have some freedom in our actions—and that that freedom can be fragile. The most fascinating thing is how the disease comes in right in the middle, an exposes the fact that our urges are not the same thing as our desires. 

Tourette Syndrome is a valuable tool in the arsenal of techniques neuroscience can use to help advance the philosophy of free will. Other ones include obsessive-compulsive disorder, addiction, and depression, all of which are associated with strong urges and thoughts that conflict with our desires.

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