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More on Personal Identity. Daniel Dennett. Co-director of the Center for Cognitive Studies at Tufts. Professor of philosophy at Tufts. One of the “Four Horsemen of the Atheist Apocalypse.”. Dennett’s Dangerous Mission.

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More on Personal Identity

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More on Personal Identity

Daniel Dennett

  • Co-director of the Center for Cognitive Studies at Tufts.

  • Professor of philosophy at Tufts.

  • One of the “Four Horsemen of the Atheist Apocalypse.”

Dennett’s Dangerous Mission

The US was trying to tunnel through the Earth to attack the Soviet Union “from below” with a nuclear weapon.

They didn’t get very far, and now the weapon is stuck under Tulsa, Oklahoma.

Dennett’s Dangerous Mission

Unfortunately, the device is emitting a special kind of radiation that completely destroys brain tissue (but no other living tissue).

Dennett is tasked with retrieving it.

First, scientists will remove Dennett’s brain.

Then, they’ll record all of it’s output signals

Then, they’ll broadcast the brain’s outputs via radio.

Finally, they’ll hook Dennett’s body up to respond to the output signals.

Also, Dennett’s nerves/ sensory organs will broadcast the brain’s inputs back to it.

Dennett’s New Life

  • Not much difference in experience.

  • If Dennett’s body is far away from his brain, then there may be a signal lag (because the speed of light is not infinite).

  • Dennett can’t get drunk by drinking alcohol. He could if you poured alcohol in his brain vat.

“Where Am I?”

Option 1: Dennett = Body

“In a brain transplant operation, one wanted to be the donor, not the recipient. Better to call such an operation a body transplant, in fact.” p. 220

Option 2: Dennett = Brain

Maybe, then Dennett is his brain.

A first problem is that he doesn’t seem to be over there (to himself).

But maybe that’s misleading.

Dennett says there’s another problem, though.

Suppose Dennett’s body, while under the control of his brain, goes and robs a bank.

I’m free!

I’m in jail!

Option 3: Perspective

Maybe Dennett is wherever his point of view is. So in the brain transplant case, he’s the recipient, because that’s where his point of view is (where he seems to be). And in the current case, he’s the remote-controlled body, because that’s where he seems to be.

Problems for Perspective

“Where Am I?”

Dennett concludes that “Where am I?” is a difficult question to answer.

  • It’s not “Where are all my parts?” because he knows the answer to that, but he doesn’t know where he is.

  • It’s not “Where is my point of view?” because he knows the answer to that, but he doesn’t know where he is.

The Story Continues…

Dennett goes off to fix the problem with the nuclear warhead. But the radiation is interfering with his radio signal:

  • First, he goes deaf (can’t send auditory signals back to brain).

  • Then he finds he can’t speak (can’t receive muscle instructions from brain).

  • Then he goes blind…

“Where Am I?”

“There I was, deaf, dumb, and blind, in a radioactive hole more than a mile under Tulsa. Then the last of my cerebral radio links broke, and suddenly I was faced with a new and even more shocking problem: whereas an instant before I had been buried alive in Oklahoma, now I was disembodied in Houston.” p. 224


  • Dennett was in Oklahoma at one moment.

  • Immediately thereafter he was in Texas.

  • Therefore, Dennett traveled faster than the speed of light.

  • But nothing with mass can travel faster than the speed of light.

  • Therefore Dennett has no mass.

  • Therefore Dennett is immaterial.

Dennett’s New Body

One year later, they succeed in getting Dennett a new body.

It’s not the same as the old one… but it’s close.

The researchers explain that they’ve created a computer “duplicate” of Dennett’s brain. Dennett’s body has been broadcasting “input” to both his brain and the computer brain. But the output is only controlled by his own brain. However, the scientists monitor the outputs for both and they’re exactly the same.

The Computer Brain

The scientists explain that there is a switch that Dennett can flip, which will change which source his body receives instructions from.

Dennett gives it a chance and flips the switch…

Flipping the Switch

“Nothing happened. A click and that was all.”

Two Dennetts

Dennett’s only worry is that they could hook up one of the Dennett brains (the computer one or the regular one) to some other body, and then someone else would know all of Dennett’s secrets.

Two Dennetts

Immediately, the inputs would diverge (because I’m not Dennett), and then the outputs would diverge (because what the brain decides to do depends on the information it’s getting from the environment).

Still, both bodies would behave like Dennett, and remember what Dennett remembered.

The dramatic conclusion…

The teletransporter

The Teletransporter

Argument Against: Replica = Me

Suppose the teletransporter malfunctions and fails to destroy my body, even though it succeeds at creating a new one just like it on the planet.

The Physical Spectrum

The Ship of Theseus:

The Yes/No Principle

The Yes/No Principle maintains that there is always a fact of the matter about whether I exist. We can ask of anyone who does exist: Is this person Michael? And there will either be a Yes answer or a No answer (even if we don’t know what the answer is).

Sharp Boundary

If we accept the Yes/No Principle, and we accept that my replica is not me, then we will be forced to say that there is a specific point in the Physical Spectrum where the replacement of one cell causes me to cease to exist.

No Fact of the Matter

Parfit thus rejects the Yes/No Principle. Instead, he says there are possible cases where there is no fact of the matter whether I survived or died. It’s not true that this person is me, and it’s not false either.

Personal Identity Purely Linguistic

“I may ask [in the TTP case], ‘Will that person be me?’ But that is a misleading way to put my question. It suggests that I don’t know what’s going to happen. When I know these other facts, I should ask, ‘Would it be correct to call that person me?’ That would remind me that, if there’s anything that I don’t know, that is merely a fact about our language.”

“Merely Verbal” Questions

Sometimes disagreements aren’t disagreements over facts.

Some people claim to have been electrocuted. I don’t think they have been, but not because I dispute any of their factual claims.

Comparison w/ Consciousness

If we find an intelligent alien or a robot, there is a real factual question as to whether it has conscious experiences or not. We may not be able to ever find out, but there is a real fact.

Parfit thinks this is not true in the difficult personal identity cases. There’s nothing that we don’t know.

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