A young man in a loose robe sits at a table by a window, reaching out to turn a celestial globe, with a book open before him — Johannes Vermeer, *The Astronomer*, c. 1668. Musée du Louvre, Paris. The heavens move by law, and the astronomer studies them. Is he, reaching out to turn the globe, any different?Public domain, via Wikimedia Commons.

Experiments on the will

The lab

The free will debate runs on two kinds of experiment: real ones, which test how decisions and the feeling of deciding actually work, and thought experiments, which test our concepts. Dennett argued that each should keep the other honest.

Libet's clock

In Benjamin Libet's 1983 experiment, people watched a spot circle a clock face once every 2.56 seconds, flexed a wrist whenever they felt like it, and then reported where the spot had been when they first felt the urge. Try it. Watch the spot, press the button whenever you feel like it, and remember where the spot was at the moment you decided.

Watch the spot circle. Whenever you feel like it, press the button, and remember where the spot was when you decided.

Libet found that brain activity began about half a second before the movement, and about a third of a second before people said they had decided. What that shows is disputed: see Libet, Mele, and Dennett on making yourself small.

The predictor

Press F or J (or tap the buttons) as randomly as you can, at least fifty times. A very simple program, which only remembers what you pressed after each recent run of five presses, will try to guess your next key before you press it. Versions of this game have been used by computer scientists, notably Scott Aaronson, to show how predictable "random" human choices are.

Press F or J as unpredictably as you can. The program guesses each key before you press it.

Most people are predicted well above chance, often 60 to 70 per cent of the time. Does that matter? Dennett would say not, in itself. Being predictable is no threat to freedom; we want our friends to predict that we will keep our promises. What would matter is being controlled by a predictor: someone who could use your predictability to manipulate you. That is the difference between a cause and a puppeteer.

The Game of Life

John Conway's cellular automaton, which Dennett used in Freedom Evolves. Click cells to bring them to life, then run the world. Every cell follows the same rule: a live cell with two or three live neighbours survives, a dead cell with exactly three comes alive, and every other cell dies or stays dead. Nothing random ever happens, yet stable objects, travellers and collisions emerge. See section 3 of the Dennett page for why this matters.

Click cells to toggle them, or add a pattern, then press run.

Every figure on the site

The digger waspDennett Move the cricket and watch Sphex repeat her routine.
Glider meets eaterDennett Determinism without inevitability.
Ducking the ballDennett Avoidance in a deterministic world.
Austin's puttDennett Could he have holed it?
The Valerian modelDennett Does a truly random generator add anything?
The ladder of freedomDennett From bacteria to persons.
Black's deviceFrankfurt Responsible without alternatives.
The trodden handP. F. Strawson Excuses, exemptions and determinism.
Dual controlsFischer Guidance control without regulative control.
The accumulatorMele How noise makes a readiness potential.
Five casesAristotle Force, ignorance and the voluntary.
The swerveEpicurus and Lucretius Atoms that break the bonds of fate.
The dog and the cartThe Stoics Led or dragged.
Foreknowledge and eternityAugustine Does knowing compel?
Water in a channelHobbes Free and necessary.
The thinking stoneSpinoza Conscious of the act, ignorant of the cause.
The man in chainsHume Hypothetical liberty.
Two standpoints and a turnspitKant Nature and freedom.
Two balls and a demonLaplace Determinism without predictability.
Six in the eveningSchopenhauer Doing what you will.
Divinity Avenue or Oxford StreetWilliam James Replaying the universe.
The vetoLibet "Free won't".
I SpyWegner Feeling you did what you did not do.
The regressSapolsky From a second before to millions of years.
The businesswomanKane A self-forming action.
The consequence argumentVan Inwagen Is any of it up to you?
The Basic ArgumentGalen Strawson No first, self-made self.
Professor PlumPereboom Four cases, one verdict?
The quarantine dialCaruso The least restrictive measure.
Think of a cityHarris Where did that come from?
Clocks to cloudsPopper Plastic control.
The other roadDeutsch Choices across the multiverse.
Four hard casesDo we deserve blame? Seven views give their verdicts.