What Makes Science Science? 科學跟非科學差在哪？

🔊In China Wang Chong had made the same complaint fifteen hundred years earlier. People said that thunder was the anger of Heaven and that it struck down those with hidden faults. Wang asked why, in that case, we so often hear Heaven angry and so seldom hear it pleased, and why thunder that kills no one should be angry at nothing. His rule was short: “Nothing makes a matter clearer than having an effect, and nothing settles an argument like having proof.” Both men saw that the question is how a belief is tested. Where it came from, and how many people hold it, settle nothing.

在中國，王充早一千五百年就發過同樣的牢騷。人們說，雷是天的怒氣，會擊殺有陰過的人。王充問：既然如此，為什麼我們老是聽到天發怒，卻很少聽到天高興？還有，那些沒打死任何人的雷，天是在空發什麼怒？他的規則很短：「事莫明於有效，論莫定於有證。」兩個人都看到了：問題在於一個信念是怎麼被檢驗的。它從哪裡來、有多少人相信，什麼也決定不了。

🔊The usual answer in Bacon’s day and long after was that science rests on observation, and that a theory is scientific when many observations confirm it. Karl Popper came to doubt this as a young man in Vienna in 1919. Three theories excited his friends: Marx’s theory of history, Freud’s psychoanalysis, and Alfred Adler’s psychology. Their admirers were impressed by how much these theories could explain. Whatever happened seemed to confirm them. Popper noticed that a man who pushes a child into the water and a man who dies trying to save the child could each be explained equally well by Freud and by Adler. He began to think that this apparent strength was a weakness.

在培根的時代以及之後很長一段時間，通常的答案是：科學建立在觀察上；一個理論如果有許多觀察印證它，它就是科學的。卡爾・波普 1919 年在維也納還是個年輕人的時候，開始懷疑這一點。有三個理論讓他的朋友們很興奮：馬克思的歷史理論、佛洛伊德的精神分析，以及阿德勒的心理學。這些理論的仰慕者，折服於它們能解釋的東西有那麼多。不管發生什麼事，似乎都印證了它們。波普注意到：一個把孩子推下水的人，與一個為了救那個孩子而死的人，佛洛伊德與阿德勒都能解釋得一樣好。他開始覺得，這個看起來的長處其實是弱點。

🔊That same year a fourth theory was put to a test. Einstein’s general relativity predicted that light passing near the sun would be bent by a definite amount, twice what Newton’s physics allowed. The prediction could be checked only during a total eclipse, and if the stars did not appear shifted as calculated, the theory was finished. An expedition led by Arthur Eddington photographed the eclipse of May 1919 and reported the shift. What struck Popper was the risk. Einstein had said in advance what would count against him. The others had never done so.

同一年，第四個理論接受了一次考驗。愛因斯坦的廣義相對論預測：經過太陽附近的光線會彎曲一個確定的量，是牛頓物理學所容許的兩倍。這個預測只有在日全食的時候才能查核；而如果星星看起來並沒有照計算的那樣偏移，這個理論就完了。亞瑟・愛丁頓率領的一支遠征隊，拍攝了 1919 年 5 月的那次日食，並且報告了那個偏移。讓波普印象深刻的是那份風險。愛因斯坦事先說出了什麼會算作對他不利。其他那幾位從來沒有這樣做過。

🔊From this Popper drew his criterion. A theory is scientific if it is falsifiable, which means that it forbids something. It names observations that, if they were made, would show it to be false. “All swans are white” is scientific in this sense, since one black swan refutes it. “Something good will happen to you this month” is not, because nothing that could happen would count against it. A theory that is compatible with every possible event tells us nothing about which events to expect. Confirmations are easy to find for almost any theory, as the tablets in the temple show. They count only when they come from a serious attempt to prove the theory wrong.

由此，波普引出了他的判準。一個理論如果是可否證的，它就是科學的；意思是它「禁止」了某些事。它指出了某些觀察：如果這些觀察真的出現，就顯示它是假的。「所有的天鵝都是白的」在這個意義上是科學的，因為一隻黑天鵝就駁倒了它。「這個月會有好事發生在你身上」不是；因為不管發生什麼，都不會算作對它不利。一個與所有可能的事件都相容的理論，並沒有告訴我們該預期哪些事件。幾乎任何理論都很容易找到印證，就像神廟裡的還願牌所顯示的。只有當印證來自一次認真的「想證明這個理論是錯的」的嘗試時，它才算數。

🔊The criterion carries a view of how knowledge grows. Scientists do not collect facts until a law emerges. They make bold guesses and try to knock them down, and what survives is kept for now. No amount of testing proves a theory true. Newton’s mechanics passed every test for two centuries and was then found to be an approximation. Science earns its authority through a method that exposes its errors, and a community that is rewarded for finding them. It does not claim certainty.

這個判準帶著一個「知識如何成長」的看法。科學家並不是蒐集事實，直到一條定律浮現。他們提出大膽的猜測，然後設法把它們打倒；活下來的，就暫時留著。再多的檢驗，也不能證明一個理論為真。牛頓力學兩個世紀裡通過了每一次檢驗，後來卻被發現只是一個近似。科學的權威，是靠著一套會暴露自身錯誤的方法、以及一個因為找出錯誤而得到獎賞的社群掙來的。它並不宣稱確定。

🔊Critics soon showed that the line is harder to draw than Popper hoped. A theory never faces a test alone. To predict where a planet will be seen, an astronomer needs the theory, and also assumptions about his telescope, the atmosphere, and the other bodies nearby. When a prediction fails, logic does not say which of these is at fault. In the 1840s Uranus was not where Newton’s laws said it should be. Astronomers did not give up Newton. They supposed an unseen planet, calculated its position, and found Neptune. When Mercury misbehaved in the same way they supposed another planet, named it Vulcan, and never found it. That anomaly was explained only by Einstein. The same move was a triumph once and a mistake once, and no rule could have told them apart in advance.

批評者很快就指出：這條線比波普期望的更難劃。一個理論從來不是單獨面對檢驗的。要預測一顆行星會出現在哪裡，天文學家需要那個理論，還需要關於他的望遠鏡、大氣，以及附近其他天體的種種假定。當一個預測失敗的時候，邏輯並沒有說是其中哪一個出了錯。1840 年代，天王星不在牛頓定律說它該在的地方。天文學家並沒有放棄牛頓。他們假定有一顆沒看見的行星，算出它的位置，然後找到了海王星。水星同樣不守規矩的時候，他們又假定了一顆行星，取名「祝融星」，卻始終沒有找到。那個異常，直到愛因斯坦才得到解釋。同一步棋，一次是大勝，一次是錯誤；而沒有任何規則能事先把兩者分開。

🔊Imre Lakatos concluded that single theories are the wrong unit. What should be judged is a research program over time. A healthy one keeps predicting new facts, and a degenerating one only patches itself after each failure. On this measure astrology fails. Parts of it can be tested, and controlled tests have gone against it. Its real fault is that in two thousand years it has explained nothing new, and its practitioners have shown little interest in the failures. In 1983 Larry Laudan argued that no single criterion separates science from the rest and that the search should be dropped. Most philosophers now treat “scientific” as a matter of degree and of several marks together: testable claims, attention to failures, openness to criticism, and progress.

伊姆雷・拉卡托斯的結論是：單一的理論是錯的衡量單位。該被評判的，是一個研究綱領在一段時間裡的表現。健康的研究綱領不斷預測出新的事實；退化的研究綱領，只是在每一次失敗之後替自己打補丁。用這個尺度，占星術不及格。它有些部分是可以檢驗的，而嚴格控制的檢驗結果對它不利。它真正的毛病是：兩千年來它沒有解釋任何新的東西；而它的從業者對那些失敗沒有表現出多少興趣。1983 年，賴瑞・勞丹主張：沒有任何單一的判準能把科學與其餘的東西分開；這場尋找應該放棄。現在多數哲學家把「科學的」看成程度的問題，並且是好幾個標記合在一起：可檢驗的主張、對失敗的重視、對批評的開放，以及進步。

🔊Popper’s criterion did not survive as a definition. It survives as a question that anyone can put to a claim, and to himself: what would show that this is wrong? A person who cannot answer, or who answers “nothing,” is holding the belief in a way that learns nothing from the world. Asking for confirmations is what the mind does by nature, as Bacon said. Looking for the drowned sailors has to be learned.

波普的判準沒有作為一個定義存活下來。它存活下來的樣子，是一個問題；任何人都可以拿它來問一個主張，也問自己：什麼會顯示這是錯的？一個答不出來、或者回答「沒有任何東西」的人，是以一種「從世界學不到任何東西」的方式持有那個信念。就像培根說的，尋找印證，是心靈天生就會做的事。去找那些淹死的水手，是要學的。