威廉·斯坦利·杰文斯William Stanley Jevons

威廉·斯坦利·杰文斯的父亲是Thomas Jevons，母亲是Mary Anne Roscoe。Thomas Jevons是一名铁商，但在发明铁船以及撰写各种法律和经济主题的文章方面都表现出许多才能。Mary Anne Roscoe是历史学家杰文斯 Roscoe的女儿。Thomas和Mary Roscoe有十一个孩子，杰文斯排行第九。这个家庭是唯一神教徒，这是新教的一个自由派分支，其宗教信仰建立在理性之上，杰文斯就是在这种信仰中长大的。在杰文斯后来的著作中有非常明确的证据表明唯一神教的影响。

杰文斯于1850年被送到伦敦，成为大学学院 School的寄宿生。第二年，他年仅十六岁，就进入大学学院，打算学习化学和植物学。他后来写道，他对社会运作方式的兴趣始于他早期的学生时代，特别是因为他在城市中行走时可以观察到伦敦穷人的状况。他写道（见[5]）：-

我开始认为我能够而且应该比别人做得更多。一种模糊的渴望和决心在我心中增长。

他满怀助人之心，但其目标极为宏大，因为他想成为5：-

……强大地善，即行善，不是对一个人、十几个人或一百个人，而是对一个民族或整个世界。

1854年，他中断了在大学学院的自然科学研究，前往澳大利亚悉尼工作。他获聘为新建的澳大利亚造币厂的化验师。这项工作涉及测定硬币的重量、尺寸或成色等特性，而杰文斯之所以获得这一职位，是因为他在化学方面已展现出令人印象深刻的能力。若非家庭陷入经济困难，他在完成学位之前很可能不会对这样的职位感兴趣。他父亲的生意在1848年倒闭，而悉尼这份报酬优厚的职位对他而言太具诱惑力，难以拒绝，因为它使他能够为家庭财务做出可观的贡献。

在澳大利亚，他有大量闲暇时间，却几乎无事可做，因此他在那里度过的五年对他的心智发展至关重要。杰文斯对气象学（就此写了一篇论文）、地质学和政治经济学产生了兴趣。他对经济学越来越感兴趣，然而这完全是一门他自学而成的学科。1858年2月，仍在澳大利亚的他写信给远在英格兰的姐姐5：-

我很高兴你觉得政治经济学尚可忍受。《国富论》也许是这个主题上最枯燥的书之一。你会看出，从科学角度说，经济学是一门非常狭隘的科学，它实际上是一种模糊的数学，计算人类勤劳的原因与结果，并表明如何最好地运用它。

在这封信中，杰文斯接着表达了与他学生时代所感受到的同样的使命感5：-

我有一个想法……我对人类知识的基础和本质的洞察比大多数人或作家都要深刻。事实上，我认为致力于这样的课题是我的使命，我打算这样做。……彻底理解社会的原则现在在我看来是最紧迫的事务。

在某种程度上，他在造币厂的工作，涉及实际制造货币，一定影响了杰文斯对经济学的兴趣，正如他父亲家族企业的失败所产生的影响一样。现在，充满了他所描述的使命感，杰文斯放弃了高薪工作，于1859年回到英国完成他的教育。回到伦敦大学学院后，他完成了学士学位，然后在1863年被授予硕士学位。在伦敦学习期间，对杰文斯的一个重要影响是奥古斯塔斯·德摩根，不是在杰文斯的经济学思想上，但肯定是在他的逻辑和probability思想上。

杰文斯对经济学的发展思想在他的通信中显而易见。1860年，当他在伦敦学习时，杰文斯写信给他的兄弟说，他最近发现了[5]：-

……我毫不怀疑这是真正的经济理论，如此彻底和一致，以至于我无法不愤怒地阅读关于这个主题的其他书籍。

在给他兄弟的同一封信中，他概述了他的想法：-

最重要的公理之一是，随着一个人必须消费的任何商品的数量，例如普通食物，增加，从最后使用的部分获得的效用或利益程度减少。

他在General Mathematical Theory of Political Economy中概述了这些关于价值边际效用理论的思想，并于1862年向英国协会 for the Advancement of Science宣读（该文于1866年发表）。

获得硕士学位后，杰文斯被任命为欧文斯学院的导师，该学院后来成为曼彻斯特大学。1865年，他被任命第二个职位，成为利物浦女王学院逻辑学和政治经济学的兼职教授。然后，在1866年，他被任命为曼彻斯特的政治经济学讲席，以及逻辑学、心理和道德哲学的教授。

1867年，杰文斯与托马斯·哈里奥特安·泰勒结婚，她是《曼彻斯特卫报》创始人和第一任编辑的女儿之一（该报于1821年创刊时为周报，1855年成为日报）。他们有三个孩子，一个儿子赫伯特杰文斯追随父亲的脚步，成为著名的经济学家。

杰文斯一直留在曼彻斯特，直到1876年他搬到伦敦大学学院。他在曼彻斯特的时光是极其多产的。他于1864年出版了Pure Logic，开发了“逻辑钢琴”，并于1870年在皇家学会展出，他于1871年出版了The Theory of Political Economy。他于1872年当选为皇家学会会士。我们应该对这些成就中的一些再多说一点。

杰文斯在经济学之外的主要贡献是在数理逻辑方面。是乔治·布尔，特别是他的书The Laws of Thought（1854年），强烈影响了杰文斯关于数理逻辑的想法。一方面，杰文斯可以被视为乔治·布尔思想的坚定支持者，并且是既致力于改进它们又将它们带给更广泛受众的人。另一方面，他自己的思想版本包含某些弱点。杰文斯和乔治·布尔在1863年和1864年通信，这些通信发表在[12]中。文章[11]讨论了乔治·布尔和杰文斯的逻辑概念之间的差异。Grattan-Guinness [10]认为，他们方法之间的主要区别在于，尽管两人都相信他们在研究思维规律，乔治·布尔有一个更代数的逻辑概念，而杰文斯则认为数学从逻辑出发。杰文斯喜欢三段论方法。

杰文斯批评了乔治·布尔工作的某些方面，他写道（例如见[1]）：-

……[乔治·布尔]为其发现所披的数学外衣并不适合这些发现，而其准数学过程远比需要的复杂得多。

这在许多方面显示了杰文斯的一个弱点，即尽管他提倡对许多问题采用数学方法，但他尤其对乔治·布尔的数学缺乏理解，这表明他无法充分领会它。

“逻辑钢琴”是一台由杰文斯设计、由索尔福德一位钟表匠制造的机器，有21个键用于等式逻辑运算。它有许多后来被纳入计算机设计的特征。正如Gridgeman在[1]中所写：-

尽管它的主要价值在于辅助新逻辑学中类与命题的教学，但它实际上以超人的速度和准确性解决了问题……

他在逻辑学方面最重要的著作是Principles of science（1874年）。这部著作对概率论和逻辑学都作出了重要贡献。杰文斯在这部著作中声称，观察中的绝对精确是不可能的，理论与它所模拟的物理情况之间的完全对应也是不可能的。他强调概念之间的相互关系，而不是当时流行的更为严格的“因果”哲学。尽管这部著作包含许多创新思想，但或许其弱点可以通过他关于概率应用的一个例子来说明。

杰文斯在1873年写道，当时已知发现了64种化学元素，其中50种是金属。然后他天真地声称，下一个被发现的元素是金属的概率为$\large\frac{50+1}{64+2}\normalsize = \large\frac{17}{22}\normalsize$。读者能看出这个论证有什么问题吗？

我们已经注意到，杰文斯于1876年离开曼彻斯特，迁往伦敦大学学院。他讲课时从未感到轻松，他觉得在伦敦必须比在曼彻斯特教得更少。然而，他发现伦敦的讲席也要求他公开演讲，而他似乎越来越讨厌这一点。1880年，他辞去伦敦的讲席，以便能专注于写作。尽管多次度假试图恢复健康，他的健康状况还是恶化了。他在英格兰南部度假游泳时溺水身亡，但事故最可能的原因是他心脏病发作或中风。

杰文斯的工作受到大多数人的高度评价。约翰·梅纳德·凯恩斯在22岁第一次接触到杰文斯的著作时写道：

我确信他是这个世纪的思想家之一。他有一种奇特地令人兴奋的写作风格，只有足够优秀的人才能写出这种风格。

Hutchison在[14]中写道：

就广度、多样性、原创性和敏锐的洞察力而言，杰文斯作为经济学家、统计学家、逻辑学家和哲学家的工作属于现代最伟大的工作之列。

然而，⟦N1⟧在18中持一种不那么积极的态度。他写道：-

……杰文斯尽管试图建立统一科学，但并不是逻辑实证主义的先驱。他的机械还原论正是为这一计划服务的，而杰文斯则试图通过发展一种数论来把数学建立在逻辑之上。……他的尝试没有成功，而且……他的错误在他整个机械体系（包括他的经济学）中仍然可见。……尽管杰文斯未能成功建立统一科学，但他有缺陷的方法论却导致了统计学最早应用于社会科学之一的例子。

Stanley Jevons's father was Thomas Jevons and his mother was Mary Anne Roscoe. Thomas Jevons was an iron merchant but showed lots of talent both as an inventor of iron boats and as a writer on various legal and economic topics. Mary Anne Roscoe was the daughter of the historian William Roscoe. Thomas and Mary Roscoe had eleven children and Stanley was the ninth. The family were Unitarians, a liberal branch of the Protestant Church that bases its religious beliefs on reason, and Stanley was brought up with these beliefs. There is very clear evidence in Jevons later writings of the Unitarian influence.

Stanley was sent to London to became a boarder at University College School in 1850. In the following year, still only sixteen years of age, he entered University College with a view to study chemistry and botany. He later wrote that his interest in the way that society worked began in his early days as a student, particularly since he could observe the condition of the poor in London as he walked about the city. He wrote (see [5]):-

I began to think that I could and ought to do more than others. A vague desire and determination grew upon me.

He was filled with a desire to help but his aims were on a grand scale for he wanted to be [5]:-

... powerfully good, that is to be good, not towards one, or a dozen, or a hundred, but towards a nation or the world.

He broke off his studies of natural sciences at University College in 1854 to take a job in Sydney in Australia. He was offered a position as an assayer at the new Australian mint. This involved determining the characteristics such as weight, measure, or quality of the coinage, and Jevons was offered the post because of his already impressive abilities at chemistry. He probably would not have been interested in such a post before he had completed his degree had his family not been in financial difficulties. His father's business had collapsed in 1848 and the attractively paid post in Sydney was too tempting for him to refuse since it allowed him to contribute substantially to his family's finances.

In Australia he had much leisure time, and little to occupy that time, so the five years he spent there were important ones for his mental development. Jevons became interested in meteorology (writing a paper on the topic), geology and political economy. He became more and more interested in economics yet it was a topic in which he was entirely self-taught. In February 1858, while still in Australia, he wrote to his sister back in England [5]:-

I am glad you find political economy tolerable. The Wealth of Nations is perhaps one of the driest on the subject. You will perceive that economy, scientifically speaking, is a very contracted science, it is in fact a sort of vague mathematics which calculates the causes and effects of man's industry, and shows how it may be best applied.

In the letter Jevons then goes on to express the same feeling of mission that he felt when a student [5]:-

I have an idea ... that my insight into the foundations and nature of the knowledge of man is deeper than that of most men or writers. In fact, I think that it is my mission to apply myself to such subjects, and it is my intention to do so. ... Thoroughly to understand the principles of society appears to me now the most cogent business.

To some extent his job in the mint, involved in actually making money, must have influenced Jevons interests in economics, as must the failure of his father's family business. Now, filled with the feelings of mission he described, Jevons gave up his lucrative job and returned to England in 1859 to complete his education. Back in University College, London, he completed his B.A. and then was awarded his Master's Degree in 1863. An important influence on Jevons while he was studying in London was De Morgan, not in terms of Jevons thoughts on economics but certainly in terms of his thoughts on logic and probability.

Jevons' developing thoughts on economics are evident in his correspondence. In 1860 when he was studying in London, Jevons wrote to his brother saying that he had recently found [5]:-

... what I have no doubt is the true theory of economy, so thorough-going and consistent, that I cannot read other books on the subject without indignation.

In the same letter to his brother he outlined his ideas:-

One of the most important axioms is, that as the quantity of any commodity, for instance plain food, which a man has to consume, increases, so the utility or benefit derived from the last portion used decreases in degree.

He outlined these ideas on the marginal utility theory of value in General Mathematical Theory of Political Economy which he read to the British Association for the Advancement of Science in 1862 (it was published in 1866).

After being awarded his Master's Degree, Jevons was appointed as a tutor at Owens College, which went on to become the University of Manchester. He was appointed to a second post in 1865 when he became a part-time professor of logic and political economy at Queen's College, Liverpool. Then in 1866 he was appointed to a chair of political economy at Manchester and also to a professorship in logic and mental and moral philosophy.

In 1867 Jevons married Harriot Ann Taylor, one of the daughter's of the founder and first editor of the Manchester Guardian (founded in 1821 as the weekly, it had become a daily paper in 1855). They had three children, one son Herbert Stanley Jevons following in his father's footsteps and becoming well known as an economist.

Jevons remained in Manchester until he moved to University College, London in 1876. His time at Manchester was a highly productive one. He published Pure Logic in 1864, developed the 'logical piano' which was exhibited at the Royal Society in 1870, and he published The Theory of Political Economy in 1871. He was elected a fellow of the Royal Society in 1872. We should say a little more regarding some of these accomplishments.

Jevons's main contributions outside economics are in mathematical logic. It was Boole, particularly with his book The Laws of Thought (1854), who strongly influenced Jevons' ideas on mathematical logic. On the one hand Jevons can be seen as a strong supporter of Boole's ideas, and someone who both worked on improving them and bringing them to a wider audience. On the other hand his own version of the ideas contained certain weaknesses. Jevons and Boole corresponded in 1863 and 1864, and this correspondence is published in [12]. The article [11] discusses the differences between Boole's and Jevons' concepts of logic. Grattan-Guinness [10] suggests that the main difference between their approach was that, although both believed they were studying the laws of thought, Boole had a more algebraic concept of logic while Jevons argued that mathematics proceeds from logic. Jevons was fond of syllogistic methods.

However, Jevons criticised certain aspects of Boole's work writing that (see for example [1]):-

... the mathematical dress into which [Boole] threw his discoveries is not proper to them, and his quasi-mathematical processes are vastly more complicated than they need have been.

In many ways this showed one weakness that Jevons had, namely that although he was advocating a mathematical approach to many problems, his lack of understanding of Boole's mathematics in particular shows that he could not fully appreciate it.

The 'logical piano', a machine designed by Jevons and constructed by a Salford watchmaker, had 21 keys for operations in equational logic. It has many features which were later incorporated into computer design. As Gridgeman writes in [1]:-

Although its principal value was as an aid to the teaching of the new logic of classes and propositions, it actually solved problems with superhuman speed and accuracy ...

His most important book in logic was Principles of science (1874). This work made important contributions to probability as well as to logic. Jevons claims in this work that absolute precision in observations is impossible, as is a complete correspondence between a theory and the physical situation that it models. He stresses the interrelation between concepts rather than the more strictly 'cause and effect' philosophy which was then current. Although the work contains much in the way of innovative ideas perhaps its weaknesses are illustrated by one of his examples on the use of probability.

Jevons, writing in 1873, knew 64 chemical elements had been discovered of which 50 are metals. He then naively claims that the probability that the next element discovered will be a metal is $\large\frac{50+1}{64+2}\normalsize = \large\frac{17}{22}\normalsize$. Can the reader see what is wrong with this argument?

We have already noted that Jevons left Manchester in 1876 when he moved to University College, London. He was never as ease when lecturing and he felt that he would have to teach less in London than Manchester. However, he found that the London chair also required him to speak in public which he seemed to hate more and more. He resigned his chair in London in 1880 so that he might concentrate on writing. His health deteriorated despite many holidays in which he tried to recover. He drowned while swimming when on holiday in the south of England, but the most likely cause of the accident was that he suffered a heart-attack or stroke.

Jevons' work is very highly regarded by most. Keynes, on first meeting Jevons' writings when he was 22 years of age wrote:-

I am convinced that he was one of the minds of the century. He has the curiously exciting style of writing which one gets if one is good enough.

Hutchison writes in [14]:-

For breadth, variety, originality, and incisive penetration, Jevons' work as economist, statistician, logician, and philosopher is among the greatest on modern times.

However, Mosselmans in [18] takes a somewhat less positive attitude. He writes:-

... Jevons was not a precursor of logical positivism despite his attempt to build up a unified science. His mechanical reductionism was directed towards this project, and Jevons tried to found mathematics on logic through the development of a theory of number. ... his attempts were unsuccessful, and ... his errors remain visible within the totality of his mechanical system, including his economics. ... Although Jevons did not succeed in establishing a unified science, his flawed methodology resulted in one of the first applications of statistics to the social sciences.