John Herschel (7 March 1792 – 11 May 1871) was an English polymath, mathematician, astronomer, chemist, inventor, experimental photographer, and philosopher of science.
In the 17th century, the “method of hypothesis” (i.e. the hypothetico-deductive method) was popular, but by the 1720s and 1730s it had lost its influence and was replaced by slow, careful inductive methods in the wake of Newton’s Principia.1 This view was still largely in effect when John Herschel was born in 1792 into a preeminent English scientific family, his father William being a prominent astronomer who is credited with discovering Uranus. He became one of the most respected scientists of his time, and in 1830s England, “one answer to the question of how to be scientific might [have been], ‘Be as much like Herschel as possible.’”2 He excelled in pure mathematics, optics (he was a pioneer in the technology leading to photography), astronomy and botany (among others). The inductive method of the day remains apparent in influencing Herschel’s work, but he deviates from it in notable ways, resulting in him being part of the movement which revived the method of hypothesis. This movement began in the mid-1700s with scientists like David Hartley and George LeSage who put forward physical theories on psychology and on the ether, respectively. Their theories were reliant on unobservable entities, and were criticized at the time not for their substance, but for their epistemological basis.1 Both fought back against this inductivist attack on their work, particularly LeSage, who proposed his own “method of hypothesis” in a series of philosophical essays, in which he contended that Newton’s work was riddled with hypotheses, contrary to the inductivism of the time.1 Following LeSage, Jean Senebier, a pioneer of photosynthesis research, advocated for the method of hypothesis in his 1775 L’Art d’observer (later revised in 1802).1 Dugald Stewart, a prominent Scottish philosopher and mathematician, wrote similarly to LeSage and Senebier, directly influencing Herschel and William Whewell (a friend and colleague of Herschel’s).3 This movement was influenced partly by scientific theories developed in the mid-late 18th century like the wave theory of light, the theory of phlogiston, and Franklin’s fluid theory of electricity, each of which hypothesized unobservables to explain observable phenomena.1 In other words, these hypotheses decidedly did not come from the aforementioned slow and cautious inductive methods. Given the apparent success of at least the wave theory of light, they had to be pursued, if not necessarily accepted, as scientific theories. And this is where the method of hypothesis, aided by Herschel and his contemporaries/immediate predecessors, came back to become the dominant scientific method.1
In 1831, Herschel published Preliminary Discourse on the Study of Natural Philosophy (PD), his most prominent work in a brief foray into the philosophy of science. Due to his breadth of study, his contribution to this field was mostly limited to his PD, a compact description of his views on the goal of science, theory construction and theory appraisal. Some authors have also compared the methods outlined therein to Herschel’s actual conduct in his scientific endeavors to ascertain his true beliefs on the scientific method, as opposed to the idealized version presented in PD. The sections of PD most relevant to scientific change are parts II and III in which Herschel shares his views on the general concept of a “cause”, on the origin of hypotheses and theories (between which he rarely distinguishes), and on the importance of the deductive appraisal of these theories.
On Causes and the Goal of Science
Herschel’s idea of the goal of science is to identify the causes behind the phenomena under investigation - not unlike many of his predecessors. Indeed, Herschel’s philosophy of science as portrayed in PD appears at first to be straightforward Humean empiricism.2 Upon closer examination, however, some ambiguities and subtleties appear. For one, the meaning of the word “cause” in the above-stated goal is unclear - Ducasse identified four possible meanings, but the most accessible and important are the concepts of a “proximate” versus an “ultimate” cause.24 An ultimate cause is one which, when arrived at, cannot be improved upon in terms of explanatory power, and truly describes the source of the phenomenon in question. A proximate cause can be improved upon, and only practically describes the phenomenon. Herschel’s goal is to identify the ultimate causes, though it is unclear whether he believes we can achieve this. In parts of PD, he states that “increasing knowledge only shows us the infinite complexity which both destroys and earthly hope of understanding the totality of the system and simultaneously assures us that the progress of our knowledge can continue forever”, and that we must “limit our view to that of laws, and to the analysis of complex phenomena by which they are resolved into simpler ones, which, appearing to us incapable of further analysis, we must consent to regard as causes.”25 But in other parts, he suggests that we may somehow be able to approach these ultimate causes, saying that sometimes, in the face of overwhelming evidence in support of a hypothesis, “we are compelled to admit one of two things: either that it is an actual statement of what really passes in nature, or that the reality, whatever it be, must run so close a parallel with it, as to admit of some mode of expression common to both”.5 Herschel thus believes in ultimate causes, and is pessimistic about our capability to reach them - but he thinks that they can be approached and that we are able to tell when we are getting closer. Herschel’s methodology of science now becomes clear - a scientist is to strive for the ultimate cause of a phenomenon, regardless of whether it is possible or not, and this will guide them on the proper path towards an explanation. It is crucial that Herschel believes that sometimes we can say we are approaching or close to ultimate truth, because otherwise this formulation of the aim of science would not be instructive at all. As for how best to do this, we must examine Herschel’s views on theory construction and evaluation.
On Theory Construction
Herschel outlines two methods of science in his Preliminary Discourse - the inductivist method towards the beginning, and the method of hypotheses in later parts. In the beginning he follows the Baconian tradition and advocates for a safe path of induction in which a scientist must reject a method of hypothesis in which a proposed theory is not adequately connected to the phenomena in question.6 In developing a hypothesis/theory, one must consider the results of the earlier inductive stages of inquiry, and cannot simply use “unrestrained [...] imagination”.5 After a hypothesis is arrived at in an appropriate fashion, one can go on to the important deductive stage of an investigation to “verify the provisional conclusions they have derived”.6
It is valid, however, to question Herschel’s commitment to this “novice” method (as some authors have labeled it) - he seems to allow for wilder speculation in his method of hypotheses (i.e. his “expert” method), and some have said that the novice method was outlined mainly for rhetorical purposes and that Herschel’s true views were more closely aligned with a more liberal, less restrictive set of guidelines. Bolt claims that Herschel “explicitly encourages and defends the use of hypothetical reasoning” in PD and in related essays, meaning that he did not feel bound to the naive inductivist view outlined above.7 This was influenced in part by the great success of the wave theory of light, which was a prime example of a theory which could not have come from purely inductive generalizations (whereas Newton’s theory of gravity is an example of one which could have).1 In this sense, Herschel contributed to the rise of the hypothetico-deductive method in the 19th-century.
Herschel’s view on theory construction and the ways in which he related to the two conflicting views of his time are nicely outlined by the first and second points of the following passage from PD:
We have next to consider the laws which regulate the action of these our primary agents; and these we can only arrive at in three ways : 1st, By inductive reasoning; that is, by examining all the cases in which we know them to be exercised, inferring, as well as circumstances will permit, its amount or intensity in each particular case, and then piecing together, as it were, these disjecta membra, generalizing from them, and so arriving at the laws desired ; 2dly, By forming at once a bold hypothesis, particularizing the law, and trying the truth of it by following out its consequences and comparing them with facts; or, 3dly, By a process partaking of both these, and combining the advantages of both without their defects, viz. by assuming indeed the laws we would discover, but so generally expressed, that they shall include an unlimited variety of particular laws ; following out the consequences of this assumption, by the application of such general principles as the case admits; comparing them in succession with all the particular cases within our knowledge ; and, lastly, on this comparison, so modifying and restricting the general enunciation of our laws as to make the results agree.5
The third point regards the deductive process of rigorously testing proposed hypotheses, which he regarded as the “essential vehicle of scientific advance”.6
On Theory Appraisal
Herschel’s views on theory appraisal closely mirror the “deductive” part of the hypothetico-deductive method. When considering a scientific theory, he states that “it is the verification of [the inductions in question] which constitutes theory in its largest sense”.5 The method of verification is described by means of an example - Herschel describes the process as follows: 1. The construction of the theory: “Inductions drawn from the motions of the several planets about the sun [lead] us to the general conception of an attractive force exerted by every particle of matter in the universe on every other”.5 2. The verification of the theory: “When we would verify this induction, we must set out with assuming this law, considering the whole [solar] system as subjected to its influence and implicitly obeying it, and nothing interfering with its action;” and when observing what formerly qualified as exceptions to the accepted theory, we find that these deviations are “neither exceptions nor residual facts, but fulfilments of general rules, and essential features of the statement of the case, without which our induction would be invalid, and the law of gravitation positively untrue.”5
In other words, a scientist must assume a proposed law, and test for deviations in an isolated environment. What we can glean from this description is that Herschel thinks a theory is “good” if it has new empirical content, and that if a theory has exceptions in a given domain, it is “positively untrue”, which is consistent with his view on the attainability of ultimate causes.
Herschel’s PD was for the most part well-received by his contemporaries, likely in part due to his high standing in the scientific and philosophical community at the time. It was praised not necessarily for its strength of argumentation (after all, Herschel was not a professional philosopher), but for its practical advice and its portrayal of the ideas of an actual practitioner of science. Darwin even cited it as a personal influence in his autobiography and referenced Herschel in the preface to his Origin. Herschel did face some criticism from William Whewell, who commented that Herschel’s departure from pure inductivism could “foster a spirit of gratuitous theorizing, which will misemploy the cultivators of science, and mislead those who learn it through words alone”.8 However, most views along these lines were silenced in the early 20th century with the acceptance of Einstein’s theory of relativity, which was arrived at partly through Whewell’s feared “gratuitous theorizing”. Overall, criticism was limited due to the scientific environment at the time, in which many speculative theories were experiencing experimental success and gaining acceptance.
Here are the works of Herschel included in the bibliographic records of this encyclopedia:
- Herschel (1831): Herschel, John. (1831) A Preliminary Discourse on the Study of Natural Philosophy. A. & R. Spottiswoode, New-Street-Square. Retrieved from https://archive.org/details/preliminarydisco00hers_0.
- Herschel (1832): Herschel, John. (1832) Mrs. Somerville's Mechanism of the Heavens. Quarterly Review 47, 537-559.
- Herschel (1833): Herschel, John. (1833) A Treatise on Astronomy. Longman, Rees, Orme, Brown, Green, & Longman, and J. Taylor. Retrieved from https://archive.org/details/treatiseonastron00hersuoft.
- Herschel (1845): Herschel, John. (1845) Report of a Commitee [...] for Revising the Nomenclature of Stars. Report of the British Association for the Advancement of Science 14, 32-42. Retrieved from https://www.biodiversitylibrary.org/item/47344#page/86/mode/1up.
- Herschel (1846): Herschel, John. (1846) Address of the President. Report of the British Association for the Advancement of Science 15, xxvii-xliv. Retrieved from https://www.biodiversitylibrary.org/item/46638#page/31/mode/1up.
- Herschel (1849): Herschel, John. (1849) Outlines of Astronomy. London Longmans, Green. Retrieved from https://archive.org/details/outlinesofastron00hersuoft.
- Herschel (1857): Herschel, John. (1857) Essays from the Edinburgh and Quarterly Reviews. Spottiswoode and Co.. Retrieved from https://archive.org/details/essaysfromedinbu00hersiala.
- Herschel (1868): Herschel, John. (1868) The Reverend William Whewell, DD. Proceedings of the Royal Society of London 65, li-lxi.
- Herschel (1869): Herschel, John. (1869) On the Theory of Probabilities. Journal of the Institute of Actuaries and Assurance Magazine 15 (3), 179-218.
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- Laudan, Larry. (1981) Science and Hypothesis. Historical Essays on Scientific Methodology. D. Reidel Publishing Company.
- Cannon, Susan Faye. (1961) John Herschel and the Idea of Science. Journal of the History of Ideas 22 (2), 215-239.
- Olson, Richard S. (1975) Scottish Philosophy and British Physics, 1750-1850: Foundations of the Victorian Scientific Style. Princeton University Press.
- Ducasse, Curt John. (1960) John F. W. Herschel's Methods of Experimental Inquiry. In Madden (Ed.) (1960), 153-182.
- Herschel, John. (1831) A Preliminary Discourse on the Study of Natural Philosophy. A. & R. Spottiswoode, New-Street-Square. Retrieved from https://archive.org/details/preliminarydisco00hers_0.
- Cobb, Aaron D. (2012) Inductivism in Practice: Experiment in John F. W. Herschel's Philosophy of Science. International Journal for the History of the Philosophy of Science 2 (1), 21-54.
- Bolt, Marvin P. (1998) John Herschel's Natural Philosophy: On the Knowing of Nature and the Nature of Knowing in Early-Nineteenth-Century Britain. University of Notre Dame.
- Whewell, William. (1831) Review of J. Herschel's 'Preliminary discourse on the study of Natural Philosophy'. The Quarterly Review 45 (90), 374-407.