Can You Know What Another Mind Feels? 你能知道別人的感受嗎？

🔊The classic answer to the first question was given by John Stuart Mill in 1865. I know in my own case, he said, that a burn is followed by pain and that the pain is followed by a cry. I observe that other people have bodies like mine, and that when they are burned they cry out as I do. I conclude that the middle link is present in them as well. This is the argument from analogy, and it describes fairly well what we would say if asked to defend our belief.

對第一個問題的經典回答，是彌爾在 1865 年提出的。他說：就我自己而言，我知道燙傷之後會痛，痛之後會叫。我觀察到別人有跟我一樣的身體，被燙到的時候也像我一樣叫出聲來。我於是推斷：中間那一環，在他們身上也有。這就是「類比論證」；如果有人要我們為自己的信念辯護，我們會說的話，它描述得相當準確。

🔊Its weakness is that it is an induction from a single case. The lesson on induction showed how little we may infer from one observation. If I had opened one box and found a beetle in it, I would have poor grounds for claiming that every box in the world contains a beetle. And here the conclusion can never be checked, since I cannot open a second box. There is a further oddity. Nobody acquires the belief in this way. An infant responds to its mother’s smile long before it could notice any correlation between its own feelings and its own face, which it has never seen.

它的弱點在於：這是從單一個案做的歸納。「歸納」那一課顯示過，從一次觀察能推出的東西有多麼少。假如我只打開過一個盒子，發現裡面有一隻甲蟲，我就沒有什麼根據宣稱世界上每一個盒子裡都有甲蟲。而且在這裡，結論永遠無法檢驗，因為我打不開第二個盒子。還有一點更奇怪：沒有人是這樣得到這個信念的。嬰兒對母親的微笑有反應的時候，還遠遠不可能注意到自己的感受與自己的臉之間有什麼關聯；它從來沒看過自己的臉。

🔊Descartes saw the gap clearly. Looking down from a window at people passing in the street, he remarks in the Meditations, what he strictly sees is hats and coats, which could conceal automata. He judges that they are men. In the Discourse on Method he asked how one could tell a perfect mechanical imitation of a human being from the real thing, and proposed “two most certain tests.” A machine could never arrange words “so as appositely to reply to what is said in its presence,” and it could never act sensibly across “all the occurrences of life,” because each of its skills would need its own special mechanism. Animals, he concluded, fail both tests and are machines without thought.

笛卡兒把這道缺口看得很清楚。他在《沉思錄》裡說，從窗口往下看街上走過的人，嚴格說來他看見的是帽子與外套，底下藏的可能是自動機。是他「判斷」那些是人。在《方法論》裡，他問：一個模仿人類模仿得十全十美的機械，要怎麼跟真人分辨？他提出了「兩個最確定的檢驗」。機器永遠無法把字詞排列得「恰當地回應在它面前說的話」；它也永遠無法在「生活中的一切境遇」裡都做出合理的行動，因為它的每一項本事都需要一個專屬的機構。他的結論是：動物兩項檢驗都通不過，是沒有思想的機器。

🔊The passage is worth rereading today. Descartes was confident that no machine would ever pass his first test, and for more than three centuries he was right.

這段話今天值得重讀。笛卡兒很有把握，沒有任何機器通得過他的第一項檢驗；而在三個多世紀裡，他是對的。

🔊Suppose the first question is settled and other creatures do have experience. In 1974 the American philosopher Thomas Nagel asked how far our knowledge of it can go. He chose bats because they are mammals, close enough to us that few doubt they feel something, and because they perceive the world chiefly by echolocation, a sense we lack. A bat sends out high-pitched cries and builds its picture of the space around it from the echoes. We can describe this process in complete physical detail. What we cannot do, Nagel argued, is know what it is like for the bat. If I imagine hanging upside down and hearing my way through the dark, I learn what it would be like for me to behave as a bat does. The bat’s own experience has a point of view built into it, and an objective description, which is written from no point of view in particular, leaves exactly that out.

假設第一個問題解決了，別的生物確實有經驗。1974 年，美國哲學家內格爾問：我們對這種經驗的認識，能走多遠？他選了蝙蝠，因為牠們是哺乳類，跟我們夠近，很少有人懷疑牠們有某種感受；也因為牠們主要靠回聲定位來知覺世界，那是我們沒有的一種感官。蝙蝠發出高頻的叫聲，再從回聲建構出周圍空間的圖像。這個過程，我們可以用完整的物理細節來描述。內格爾論證，我們做不到的，是知道那對蝙蝠來說是什麼感覺。如果我想像自己倒掛著、在黑暗中靠聽覺找路，我得知的是：「我」表現得像蝙蝠會是什麼感覺。蝙蝠自己的經驗內建著一個觀點；而客觀的描述，是不從任何特定觀點寫成的，它漏掉的恰恰就是這個。

🔊Eight years later the Australian philosopher Frank Jackson made the point with a human being. Mary is a brilliant scientist who has lived all her life in a black-and-white room and learned about the world from black-and-white screens. Her field is color vision, and she has come to know every physical fact about it: the wavelengths, the cells of the retina, the pathways in the brain, the way people use the word “red.” One day the door is opened and she sees a ripe tomato. Does she learn anything? Most people answer that she does. She learns what it is like to see red. But she already knew all the physical facts. Jackson concluded that there are facts about experience that physics cannot state, and the argument has been disputed at every step ever since. You can try it below.

八年後，澳洲哲學家傑克森用一個人說了同樣的道理。瑪麗是一位傑出的科學家，一輩子住在一個只有黑白的房間裡，透過黑白的螢幕認識世界。她的專長是色彩視覺，而她已經知道了關於它的每一個物理事實：波長、視網膜上的細胞、腦裡的路徑、人們怎麼使用「紅」這個字。有一天門打開了，她看見一顆熟透的番茄。她學到了什麼嗎？多數人回答：學到了。她學到看見紅色是什麼感覺。可是她原本就知道全部的物理事實了。傑克森的結論是：有一些關於經驗的事實，是物理學說不出來的；而這個論證，此後每一步都有人爭論。你可以在下面親自試一次。

🔊Wittgenstein thought the whole problem rested on a wrong picture. Imagine, he says, that everyone has a box with something in it that we call a “beetle.” No one can look into anyone else’s box, and each says that he knows what a beetle is only from his own. In that situation the thing in the box would play no part in the meaning of the word. The boxes could hold different things, or nothing. His point is that words such as “pain” cannot get their meaning from a private inner object that each speaker points to alone. We learn them in public, from people who comfort us when we fall. And in ordinary life we do not infer that someone is in pain. We see it in the face, as directly as we see that the face is pale. On this view the skeptic’s picture of minds sealed inside bodies is itself the mistake.

維根斯坦認為，整個問題建立在一幅錯誤的圖像上。他說，想像每個人都有一個盒子，裡面裝著我們叫作「甲蟲」的東西。誰也看不到別人的盒子，每個人都說他只是從自己的那一隻知道甲蟲是什麼。在那種處境裡，盒子裡的東西對這個詞的意義毫無作用。各個盒子裝的可以是不同的東西，也可以什麼都沒有。他的重點是：「痛」這類的詞，不可能從每個說話者獨自指著的一個私有的內在對象得到意義。我們是在公共場合學會這些詞的，是從我們跌倒時安慰我們的人那裡學來的。而在日常生活裡，我們並不是「推論」出某人在痛。我們在臉上看見它，就像看見那張臉發白一樣直接。照這個看法，懷疑論者那幅「心靈密封在身體裡」的圖像，本身就是錯誤所在。

🔊The oldest statement of the problem is a conversation of about sixty words. Zhuangzi and his friend Huizi, a logician, were strolling on the bridge over the Hao River. Zhuangzi remarked that the minnows were swimming about freely, and that this was the happiness of fish. Huizi said: “You are not a fish. How do you know the happiness of fish?” Zhuangzi replied: “You are not I. How do you know that I do not know it?” Huizi pressed his advantage. “I am not you, so I do not know what you know. You are not a fish, so you do not know the happiness of fish. The case is complete.” Zhuangzi’s answer has been argued over for two thousand years. “Let us go back to the beginning. When you asked how I know, you already knew that I knew. I know it from up here on the Hao.”

這個問題最古老的陳述，是一段大約六十個字的對話。莊子與他的朋友、名家的惠子，在濠水的橋上散步。莊子說，鯈魚游得從容自在，這就是魚的快樂。惠子說：「子非魚，安知魚之樂？」莊子答：「子非我，安知我不知魚之樂？」惠子乘勝追擊：「我不是你，所以不知道你知道什麼；你不是魚，所以你不知道魚的快樂。這就說完了。」莊子的回答，被爭論了兩千年：「請回到開頭。你問我『怎麼知道』的時候，就已經知道我知道了。我是在濠水上面知道的。」

🔊Huizi argues as Nagel’s reader might: knowledge of an experience requires being the one who has it. Zhuangzi first shows that the principle defeats itself, since Huizi relies on knowing something about Zhuangzi’s mind in order to state it. His last line turns on the Chinese word ān, which means both “how” and “from where.” He answers the second sense. He knows it from where he stands, on a bridge, on a fine day, watching them. The suggestion is that knowledge of another creature is had from within a shared situation, by a being that is itself alive and at ease, and that no proof conducted from outside is needed or possible. Mencius, his contemporary, made a similar observation about human beings. Anyone who suddenly sees a child about to fall into a well feels alarm and compassion, and feels it before any thought of reward. For Mencius that response is the root of all morality.

惠子的論證方式，像是內格爾的一位讀者會用的：要知道一個經驗，就必須是擁有那個經驗的那一個。莊子先指出這條原則自己打敗自己，因為惠子要說出這條原則，就得靠著知道莊子心裡的某件事。他的最後一句，關鍵在「安」這個字，它既是「怎麼」，也是「在哪裡」。他回答的是第二個意思。他是從他站的地方知道的：在一座橋上，在一個好天氣裡，看著牠們。這裡的暗示是：對另一個生命的認識，是在一個共同的處境之內得到的，是由一個自己也活著、也自在的存在者得到的；從外面進行的證明，既不需要，也不可能。跟他同時代的孟子，對人類做過類似的觀察。任何人突然看見一個小孩快要掉進井裡，都會感到驚懼與不忍，而且是在想到任何好處之前就感到了。對孟子來說，那個反應是一切道德的根苗。

🔊The problem has left the seminar room. In 2012 a group of neuroscientists meeting at Cambridge signed a declaration that mammals, birds, and other creatures, octopuses among them, have the neural equipment for conscious states, and laws on animal welfare have begun to follow. In hospitals, some patients who show no response at all have been found, when placed in a scanner and asked to imagine playing tennis, to produce the same brain activity as healthy volunteers. And there are now machines that pass the first of Descartes’s tests with ease. They reply appositely to whatever is said to them, and when asked they will describe their feelings. Whether there is anything it is like to be such a system is a question on which serious researchers disagree, and no agreed method exists for settling it. In each of the three cases behavior has come apart from the usual signs, and we find that we have been relying on resemblance to ourselves without ever deciding which resemblances count.

這個問題已經離開了研討室。2012 年，一群在劍橋開會的神經科學家簽署了一份宣言：哺乳類、鳥類與其他生物（章魚也在其中）具備產生意識狀態的神經構造；動物福利的法律也已經開始跟進。在醫院裡，有些完全沒有反應的病人，被放進掃描儀、並被要求想像自己在打網球的時候，產生了跟健康受試者相同的腦部活動。而現在也有了輕易就通過笛卡兒第一項檢驗的機器。不管對它們說什麼，它們都能恰當地回應；被問到的時候，還會描述自己的感受。「當這樣一個系統」有沒有任何感覺可言？認真的研究者在這個問題上意見分歧，也還沒有一個公認的方法可以解決它。在這三種情況裡，行為都跟通常的徵象脫了鉤；而我們發現，自己一直依賴的是「跟我們相似」，卻從來沒有決定過，哪些相似才算數。