进入绪论之后的第二章，可证伪性。作者把这一部分安排在这个位置，不难推知他对可证伪性的重视。

Sentence 1

Scientific theories must always be stated in such a way that the predictions derived from them could potentially be shown to be false. Thus, the methods of evaluating new evidence relevant to a particular theory must always include the possibility that the data will falsify the theory. (Chap. 2, p. 22)

简评：非常简单直接的阐释，简单得让人想起行为主义的主张。当然，也可以作一些延伸。从这个解释出发，可以推导出科学应当具有的预测力。一些不具有可证伪性的体系，确实不具有预测力，或者具有虚假的预测力。

Sentence 2

The more specific and precise the prediction was, the more potential observations there were that could have falsified it. (Chap. 2, p. 24)

简评：这里是对一个妙趣横生的例子（朋友对敲门人的三次预测）的总结，把可证伪性的内涵进一步具体化了。

Sentence 3

Freudian theory uses a complicated conceptual structure that explains human behavior after the fact——that is, after it has occurred——but does not predict things in advance. In short, Freudian theory can explain everything. However, as Popper argued, it is precisely this property that makes it scientifically useless. It makes no specific predictions. Adherents of psychoanalytic theory spend much time and effort in getting the theory to explain every known huaman event, from individual quirks of behavior to large-scale social phenomena…Freudian psychoanalytic theory currently plays a much larger role as a spur to the literary imagination than as a theory in contemporary psychology. (Chap. 2, p. 24-25)

简评：作为弗洛伊德曾经的拥趸，我最早也是在心理学教材里认识到精神分析的问题的。对于这些指控，我基本上是比较同意的；当然，我也很讨厌网络上一些抓着这一点鞭尸的戾气谩骂。在这个问题上，可证伪性确实应当得到足够的重视，并作为防止我们落入事后智慧的陷阱中的理论支持。

Sentence 4

But the existence of such unfalsifiable theories does real damage. For example, explanations for the cause of autism were led down a blind alley by psychoanalytic explanations for the condition. Influnced by psychoanalytic ideas, psychologist Bruno Bettelheim popularized the now-discredited notion of “refrigerator mothers” as the cause and thought that “the precipitating factor in infantile autisum is the parent’s wish that his child should not exist”. Ideas like this not only did damage, but they set back the study of autism. (Chap. 2, p. 25)

简评：看到这一段还是很震惊的。在理解了精神分析的缺陷以后，我也不曾想到它在科学史上的负面影响，尽管在理想状况下它可以作为边缘的理论，供爱好者探讨分析。这样的例子或许并不会很多，但是已经足够揭示问题了。读完以后，我也想起了约翰·华生在他臭名昭著，却又意义非凡的条件作用建立恐惧的研究中张扬的宣言：（经过条件作用形成恐惧后）如果将来支持精神分析的人看到这个孩子(Alebert)对毛茸茸的东西的无端恐惧，不难想象，他们又会用精神分析的什么理论来解释(转引自Hock, 2015)。所以，确实有必要认真审视精神分析的作用。

Sentence 5

Shapiro, Shapiro, Bruun, and Sweet (1978) described one psychoanalyst who thought that his patient was “reluctant to give up the tic because it became a source of erotic pleasure to her and an expression of unconscious sexual strivings.” Another considered the tics “stereotyped equivalents of onanism…The libido connected with the genital sensation was displaced into other parts of the body.” A third considered the tic a “conversion symptom at the anal-sadistic level.” A fourth thought that a person with Tourette syndrome had a “compulsive character, as well as a narcissistic orientation” and that the patient’s tics “represent[ed] an affective syndrome, a defense against the intended affect.” (Chap. 2, p. 26)

简评：翔实而让人啼笑皆非的例子。

Sentence 6

These explanations were enticing because they seemed to explain things. In fact, they explain everything——after the fact. However, the explanations they provided created only the illusion of understanding. (Chap. 2, p. 26)

简评：一针见血。

总结

可证伪性的部分到这里还没有结束，但是这一部分已经足够让人印象深刻了。科学的漫长过去中，原来确实不乏离奇怪诞的例子。到这里，也可以比较理解可证伪性的意义了。

当然，可证伪就足够了吗？或者说，可证伪性就是唯一标准吗？好像是有许多反对声音的。而且，波普尔以后确实有更多不同的观点，我暂时还不清楚。半年前在《心理学报》上看到过一篇饱受争议的论文。这篇论文的审稿意见，可以说是我看过的最滑稽的审稿意见了，几位评审专家大发脾气，愤怒跃然纸上。心理学报公众号这篇推送的评论区，也是一片唇枪舌剑。论文里提到的一点是，后验概率也是不可证伪的，却是概率论的重要基础(舒跃育, 石莹波, & 袁彦, 2019)。有评审意见认为，这是不同范畴的内容。我大概可以理解这种“不同范畴”指的是什么，或许是类似于“极限”的，类似于数学归纳法的，在逻辑上可以认为成立的命题。不过，好像也不能认为是这样。

争论不出结果的时候，可能还是埋头工作比较实在。当然，也要保持理论的自觉。严格的可证伪性对于当代心理学来说，是重要的支撑，可能也是束缚，有点行为主义时代的遗风。不过，当算力足够强大的时候，大概就不会有这么多苦恼了吧？我不得而知。

参考文献

舒跃育, 石莹波, 袁彦. (2019). “操作性定义”和“证伪标准”不足以为心理学奠基. 心理学报, 51(9): 1068-1078.
Hock, R. R. (2015). Forty Studies That Changed Psychology. 人民邮电出版社, 7th edition: 94.