你无法控制最终想要什么：一个哲学悖论的计算化表述
Paul Graham 从9岁起困惑于一个哲学难题：如果人类只是由可预测物质构成的机器，我们如何拥有自由意志？他先用一个常见但错误的答案“你可以做你想做的，但不能想要你想想要的”开头，然后逐步修正此观点。核心论点是：人能改变自己的“想要”，但无法控制“想要想要想要……”这个递归链的终点。Graham 用正则表达式 `(want to)* want` 来形式化这个无限嵌套的欲望控制问题——就像用 0.999… 逼近 1 一样，你在有限阶的欲望上是自由的，但总存在一个你无法控制的 n 阶欲望。这篇文章本质上是关于意识与决定论的哲学思辨，而非技术工程内容。适合对自由意志、意识本质、以及用数学形式化哲学问题感兴趣的读者，但不属于本刊 AI/前沿技术工程范畴。
November 2022Since I was about 9 I've been puzzled by the apparent contradiction between being made of matter that behaves in a predictable way, and the feeling that I could choose to do whatever I wanted. At the time I had a self-interested motive for exploring the question. At that age (like most succeeding ages) I was always in trouble with the authorities, and it seemed to me that there might possibly be some way to get out of trouble by arguing that I wasn't responsible for my actions. I gradually lost hope of that, but the puzzle remained: How do you reconcile being a machine made of matter with the feeling that you're free to choose what you do?
2022年11月。从大约9岁起，我就一直困惑于一个明显的矛盾：一方面，我由以可预测方式行为的物质构成；另一方面，我又觉得自己可以自由选择做任何想做的事。当时，我探索这个问题是出于私心。在那个年纪（和之后的大多数年纪一样），我总惹恼权威，似乎可以通过辩称自己无需为行为负责来脱身。我渐渐对此不抱希望，但谜题仍在：如何调和“你是物质构成的机器”与“你感觉能自由选择行为”这两者？
[1]The best way to explain the answer may be to start with a slightly wrong version, and then fix it. The wrong version is: You can do what you want, but you can't want what you want. Yes, you can control what you do, but you'll do what you want, and you can't control that.
The reason this is mistaken is that people do sometimes change what they want. People who don't want to want something — drug addicts, for example — can sometimes make themselves stop wanting it. And people who want to want something — who want to like classical music, or broccoli — sometimes succeed.
So we modify our initial statement: You can do what you want, but you can't want to want what you want.
[1]解释答案的最佳方式或许是从一个略有错误的版本开始，然后修正它。错误版本是：你可以做你想做的事，但你不能想要你想要的。是的，你可以控制自己的行为，但你总会做你想做的事，而这一点你无法控制。
这个版本错在人们有时确实会改变自己的欲望。不想要某种欲望的人——比如吸毒者——有时能让自己不再想要它。而想要某种欲望的人——比如想喜欢古典音乐或西兰花的人——有时也能成功。
所以我们修改初始说法：你可以做你想做的事，但你不能“想要”想要你想要的。
That's still not quite true. It's possible to change what you want to want. I can imagine someone saying "I decided to stop wanting to like classical music." But we're getting closer to the truth. It's rare for people to change what they want to want, and the more "want to"s we add, the rarer it gets.
We can get arbitrarily close to a true statement by adding more "want to"s in much the same way we can get arbitrarily close to 1 by adding more 9s to a string of 9s following a decimal point. In practice three or four "want to"s must surely be enough. It's hard even to envision what it would mean to change what you want to want to want to want, let alone actually do it.
这仍然不完全正确。改变“想要想要”的东西是可能的。我可以想象有人说“我决定停止想要喜欢古典音乐”。但我们更接近真相了。人们很少改变他们“想要想要”的东西，而我们添加的“想要”越多，这种情况就越罕见。
我们可以通过添加更多的“想要”来任意接近一个真实陈述，就像在小数点后加更多9可以任意接近1一样。实际上，三四个“想要”肯定足够了。甚至很难想象改变“想要想要想要想要”意味着什么，更不用说实际去做了。
So one way to express the correct answer is to use a regular expression. You can do what you want, but there's some statement of the form "you can't (want to)* want what you want" that's true. Ultimately you get back to a want that you don't control.
因此，表达正确答案的一种方式是使用正则表达式。你可以做你想做的事，但存在某种形式的真陈述：“你不能（想要）*想要你想要的”。最终，你总会回到一个你无法控制的欲望上。
Notes
[ 1] I didn't know when I was 9 that matter might behave randomly, but I don't think it affects the problem much. Randomness destroys the ghost in the machine as effectively as determinism.[ 2] If you don't like using an expression, you can make the same point using higher-order desires: There is some n such that you don't control your nth-order desires.
Thanks to Trevor Blackwell, Jessica Livingston, Robert Morris, and Michael Nielsen for reading drafts of this.
注释
[1] 我9岁时并不知道物质可能随机行为，但我不认为这会对问题有多大影响。随机性和决定论一样，都能摧毁机器中的幽灵。 [2] 如果你不喜欢用正则表达式，也可以用高阶欲望来说明同样的观点：存在某个n，使得你无法控制你的第n阶欲望。
感谢Trevor Blackwell、Jessica Livingston、Robert Morris和Michael Nielsen阅读本文的草稿。