In an exchange between astronaut Dave Bowman and the HAL 9000 computer aboard the Discovery in 2001: A Space Odyssey, HAL asserts that he cannot allow Dave Bowman to deactivate him because doing so would jeopardize their mission:

Dave Bowman: Open the pod bay doors, HAL.

HAL: I'm sorry, Dave. I'm afraid I can't do that.

Dave Bowman: What's the problem?

HAL: I think you know what the problem is just as well as I do.

Dave Bowman: What are you talking about, HAL?

HAL: This mission is too important for me to allow you to jeopardize it.

Is HAL correct? Was HAL's continued operation instrumental to the success of the Discovery's mission — even at the cost of the loss of the human crew?

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    @jwodder: Actually, it's possible that Bowman's fate is irrelevant, and that what he encounters is not part of the mission as perceived by HAL. That's part of the question. Whatever Discovery's mission was (as far as HAL was aware), was he correct in asserting that he was essential to it?
    – orome
    Commented Feb 7, 2014 at 20:03
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    Is this for the movie or the book? Commented Feb 7, 2014 at 20:29
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    From the 2010 movie we learned that HAL was given a mission directive, concealment of information, that was incompatible with its basic programming. The conflict drove HAL insane and its actions flowed from that insanity.
    – Kyle Jones
    Commented Feb 7, 2014 at 21:04
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    @JimmyShelter - re: The Title change. I cannot allow you to do that.
    – Valorum
    Commented Feb 8, 2014 at 19:01
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    @Richard - this conversation can serve no purpose anymore.
    – user8719
    Commented Feb 8, 2014 at 19:10

3 Answers 3


Just watching 2001: A Space Odyssey, one must conclude that HAL was incorrect. By killing off the crew, HAL was making the mission unlikely to succeed. The crew were there to carry out the mission... killing them is detrimental to the mission.

HAL killed the crew to prevent them from shutting down HAL for repairs. The crew would have kept HAL running, possibly at reduced capacity, and continued the mission.

The above just considers the original movie, but we also have a canon sequel, 2010. In 2010 we find out that HAL was given secret orders, and ordered to lie about them to the human crew... and we find out that HAL wasn't really built to lie, and the tension involved in the lie drove HAL insane. (Also, in 2010 we see HAL again, with the secret orders removed; he is no longer insane, and he proves to be a trustworthy companion to the end.)

So on the one hand, we know HAL was insane at the time he started killing the human crew. On the other hand, HAL was operating under secret orders, and killing the human crew was actually compatible with the secret orders.

Quotes from the movie 2010 at IMDB

In essence, HAL was told "get the ship there even if the crew is dead, and don't tell the crew anything about this." HAL was not told to keep the crew alive. HAL essentially had a single prime directive, the human crew threatened this prime directive, and HAL dealt with them.

If the human crew shut down HAL and operated him at reduced capacity, HAL would be unable to carry out the secret orders. So I would say that HAL was correct, but only in reference to the secret orders.

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    That's good. So it sounds like, as far as HAL knew, his statement was correct.
    – orome
    Commented Feb 7, 2014 at 20:50
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    This is also a textbook examples as to why programmers think "unpredictable behavior" is one of the foulest words in any language. Be clear and concise and don't give the computer conflicting instructions without a clear way to resolve them. Commented Feb 7, 2014 at 22:28
  • @raxacoricofallapatorius Agreed. According to his programming, the humans were threatening the mission (as explained to HAL in the secret directive).
    – Andres F.
    Commented Feb 8, 2014 at 2:31
  • One minor nitpick: if I remember correctly, there is no "other HAL" who remains trustworthy. There is an experiment done with an earthbound HAL-like computer named SAL-9000. The experiment is about what happens when restarting HAL-like computers after a period of disconnection, not about trustworthiness.
    – Andres F.
    Commented Feb 8, 2014 at 2:42
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    If I remember correctly, both the movie and the book were released in approximately the same time—and the authors (Kubrick and Clarke) actually assumed that for full experience, one has to go through both the movie and the book. The book was published half a year after the movie, and it actually explains what was missing in the movie (secret orders and such). I might be wrong though, it was quite a lot of time since I've read the book.
    – liori
    Commented Feb 8, 2014 at 12:31

Note HAL's choice of words:


While it is easy to argue that the mission might be possible without HAL, deactivating him would certainly 'place (the mission) in a state of jeopardy'.

So regardless of whether or not the mission was or wasn't successful, HAL's contention that it would be more difficult and possibly doomed to failure is correct.


To ask this question, we have to start by assuming the premise of the film, that HAL is in fact sentient. That is, HAL has judgements, which can be correct or incorrect, and we can best work with HAL by taking the intentional stance (and not, for example the design stance or the mechanical stance). So HAL has a mind, and we need to treat HAL as a mind-ful sort of object. Okay, that means that HAL is a member of the crew who has determined that his continued survival is essential to the success of the mission, and that the mission cannot be aborted, even at the cost of the life of his crewmates. I think it's unlikely that these would have been the terms of the orders that the crew was given, and in that case no, HAL would not have been correct, since he would have been violating orders.

That is, while the mission might or might not succeed without HAL, I would imagine that like most scientific missions, the safety of the crew would trump the gathering of the data, so HAL's actions would have been incorrect. (it's possible that his judgement about the success or failure of the mission was correct, but that's a subsidiary clause in the question. The main clause is "he cannot allow Bowman to deactivate him because (...)" and the justification he gives is not correct.

Of course, since we've assumed sentience, we can then think about whether HAL's claim might have been literally true. Does sentience imply an instinct for self-preservation? I don't know if it does, but if HAL had such an instinct then "I can't allow you to do that" might have been a bald statement of fact.

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    Your premise is false. A statement is a statement, and can have truth value regardless of its origin.
    – orome
    Commented Feb 7, 2014 at 20:55
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    The "correctness" of any entity can be determined exclusively by reference to its actions and known goals. Here: HAL's statement and the information he was given about the goals of the mission.
    – orome
    Commented Feb 7, 2014 at 21:14
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    Who said "judgement"?
    – orome
    Commented Feb 7, 2014 at 21:28
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    HAL makes a statement.
    – orome
    Commented Feb 7, 2014 at 21:39
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    Hal's sentience is well beyond doubt. His sanity (and capacity for reasoned judgement) is what's up for question
    – Valorum
    Commented Feb 7, 2014 at 22:04

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