Borrowed Terms and Innovative Concepts in Newton’s Natural Philosophy
Kirsten Walsh writes…
In my last two posts, I have discussed my alterations to the 20 theses of our project. In this post, I’ll continue to discuss thesis 8.
In 2011, I claimed that:
- 8. The development of Newton’s method from 1672 to 1687 appears to display a shift in emphasis from experiment to mathematics.
But at the start of this year, I replaced this thesis with a new thesis 8:
- 8. In his early work, Newton’s use of the terms ‘hypothesis’ and ‘query’ are Baconian. However, as Newton’s distinctive methodology develops, these terms take on different meanings.
In my last post, I told you that I decided to remove my original thesis 8 because the methodological differences between Newton’s early papers and Principia aren’t as great as I initially thought. This isn’t to say that I now think that the methodology of the 1672 paper is precisely the same as the methodology displayed in Principia. Rather, I don’t think my original thesis 8 captures what is important about these differences.
In today’s post, I’ll tell you about my new thesis 8.
On this blog, we have argued that the early members of the Royal Society adopted the new experimental philosophy in a Baconian form. Newton initially encountered the experimental philosophy in the early- to mid-1660s through his reading of Boyle, Hooke and the Philosophical Transactions. While he never adopted the Baconian method of natural history, other features of his early methodology resemble the Baconian approach. For example, in Newton’s 1672 paper and the debate that followed, his use of experiment and queries, and his anti-hypothetical stance, were recognised and accepted by the Baconian experimental philosophers. Moreover, his 1675 paper, in which he explored his hypothesis of the nature of light, was recognised by his contemporaries as an acceptable use of a hypothesis.
In Newton’s later work, however, hypotheses and queries look quite different.
Firstly, consider Newton’s Opticks. When the Opticks was published in 1704, it contained no hypotheses, and the introduction explicitly stated that:
- “My Design in this Book is not to explain the Properties of Light by Hypotheses, but to propose and prove them by Reason and Experiments.”
Book III ended with a series of queries, which provided directions for further research, in the style of Baconian queries. E.g.:
- “Query 2. Do not the Rays which differ in Refrangibility differ also in Flexibility…?”
However, in the 1706 and 1718 editions, Newton introduced new queries, which explore the nature of light. E.g.:
- “Qu. 29. Are not the Rays of Light very small Bodies emitted from shining Substances?”
Like the earlier queries, these ones set out a new research program. But they are much more speculative than was acceptable according to the Baconian method.
Now consider Newton’s Principia. There are hypotheses in every edition of Principia, but they look nothing like Newton’s 1675 hypothesis. In particular, they do not explore the nature of things. For example:
- “Hypothesis 1. The centre of the system of the world is at rest.”
I have argued that the hypotheses in Principia provide a specific supportive role to theories. These propositions are temporarily assumed in order to draw out the observational consequences of Newton’s theory of gravitation. They are simplifying assumptions; not assumptions about the nature of gravity.
Previously, I have argued that Newton’s methodology should be seen as a three-way epistemic distinction between theories, hypotheses and queries. I call this an ‘epistemic triad’. I claim that Newton took these, already familiar, terms and massaged them to fit his own three-way epistemic distinction. It is important to recognise, therefore, that the triad is a three-way epistemic division, rather than the juxtaposition of three terms of reference. The terms ‘theory’, ‘hypothesis’ and ‘query’ are simply labels for these epistemic categories.
In fact, this is a feature of many of Newton’s innovative concepts. He borrowed familiar terms and massaged them to fit his own needs. I have shown that he did this with his key methodological terms: ‘theory’, ‘hypothesis’ and ‘query’. Steffen Ducheyne has argued that Newton did this in other aspects of his methodology, such as his dual-methods of analysis and synthesis. This suggests that Newton’s labeling and naming of things was very much post hoc. It seems that, when discussing Newton’s methodology, we should emphasize divisions and functions over definitions.
Hypotheses and political philosophy: Tenison against Hobbes
Peter Anstey writes …
Our research project at Otago on experimental philosophy has largely focused on natural philosophy. However, while early modern experimental philosophy had its origins in natural philosophy in mid-seventeenth-century England, it quickly impacted on other disciplines.
Tenison (1636-1715)
Experimental philosophers, as we have repeatedly stressed in previous posts on this blog, regarded Francis Bacon as their progenitor and promoted observation and experiment and decried speculation and the use of hypotheses and premature system building.
It is of great interest, therefore, to find elements of the method of experimental natural philosophy being applied as early as 1670 in an attack on Thomas Hobbes’ doctrine of the state of nature. The divine Thomas Tenison in his The Creed of Mr Hobbes examined, London, 1670, attacked Hobbes’ doctrine of the state of nature for being the product of Hobbes’ own imagination. Hobbes postulated in his Leviathan (1651) that before the existence of civil society all people were in a state of ‘warre, as is of every man, against every man’’ in which life is ‘solitary, poore, nasty, brutish, and short’. Here is how Tenison attacks him:
It is a very absurd and unsecure course to lay the ground-work of all civil Polity and formed Religion, upon such a supposed state of Nature, as hath no firmer support than the contrivance of your own fancy. (p. 131)
For Tenison, it is one thing for the various competing cosmological hypotheses of Ptolemy, Tycho, Copernicus and Descartes to be entertained, for, even if none of these happens to be true, ‘the interests of Men remain secure’. But it is another thing entirely to found the doctrines of civil, moral and Christian philosophy on ‘Hypotheses, framed by the imagination’. Tenison continues:
such persons who trouble the World with fancied Schemes and Models of Polity, in Oceana’s and Leviathans, ought to have in their Minds an usual saying of the most excellent Lord Bacon concerning a Philosophy advanced upon the History of Nature. That such a work is the World as God made it, and not as Men have made it: for that it hath nothing of Imagination. (pp. 131–2)
Hobbes (1588-1679)
Note the appeal to Bacon, the reference to natural history and the criticism of philosophy based upon fancies. (Note too the reference to James Harrington’s The Commonwealth of Oceana, 1656.) And yet Tenison does not appeal to observation and experiment because Hobbes’ doctrine as he conceives it is about a past state in human history. Instead he believes that civil philosophy should use ‘reason assisted with Memory touching the passed state of the World’ (p. 131).
What I would like to know is whether this the first use of aspects of the method of experimental philosophy to critique political philosophy?
Emilie du Châtelet on Hypotheses
Kirsten Walsh writes…
Emilie Du Châtelet (1706-1749) is best known in the popular literature as one of Voltaire’s lovers, but among her contemporaries, she was considered to be a brilliant mathematician, physicist and philosopher, whom Voltaire once described as “a great man whose only fault was being a woman”. Her work on heat and light predicted infrared radiation, and her translation and commentary of Newton’s Principia, published ten years after her death, is still considered to be the standard French translation. Today I’m interested in Du Châtelet’s views on hypotheses.
Emilie Du Châtelet (1706-1749)
Du Châtelet’s lengthiest discussion of the use of hypotheses in natural philosophy is found in her Institutions de Physique* (1740), which she wrote as a textbook for her thirteen year old son. Here, Du Châtelet explicitly set up her position on hypotheses in opposition to both Descartes and the Newtonians. She saw both positions as too extreme; and neither position as correct or useful. On the one hand:
- “Descartes, who had established much of his philosophy on hypotheses, … gave the whole learned world a taste for hypotheses; and it was not long before one fell into a taste for fictions. Thus, the books of philosophy, which should have been collections of truths, were filled with fables and reveries.”
But on the other hand, those who follow Newton “have fallen into the opposite excess”:
- “…he alone, who was able to assign and demonstrate the causes of all that we see, would be entitled to banish hypotheses from physics; but, as for us, who do not seem to be cut out for such knowledge, and who can only arrive at the truth by crawling from probability to probability, it is not for us to pronounce so boldly against hypotheses.”
Du Châtelet advocated a more moderate position. She thought that hypotheses performed several important functions:
Firstly, hypothesising is a good way to get the proverbial ball rolling. She wrote:
- “There must be a beginning in all researches, and this beginning must almost always be a very imperfect, often unsuccessful attempt. There are unknown truths just as there are unknown countries to which one can only find the good route after having tried all the others. Thus, some must run the risk of losing their way in order to mark the good path for others; so it would be doing the sciences great injury, infinitely delaying their progress, to banish hypotheses as some modern philosophers have.”
Secondly, hypotheses can provide useful explanations of the phenomena:
- “When certain things are used to explain what has been observed, and though the truth of what has been supposed is impossible to demonstrate, one is making a hypothesis. Thus, philosophers frame hypotheses to explain the phenomena, the cause of which cannot be discovered either by experiment or by demonstration.”
So, unlike Newton, Du Châtelet thought that, if we couldn’t obtain certainties, then we should make do with probabilities:
- “The true causes of natural effects and of the phenomena we observe are often so far from the principles on which we can rely and the experiments we can make that one is obliged to be content with probable reasons to explain them. Thus, probabilities are not to be rejected in the sciences, not only because they are often of great practical use, but also because they clear the path that leads to truth.”
Thirdly, hypotheses suggest new experiments:
- “Hypotheses must then find a place in the sciences, since they promote the discovery of truth and offer new perspectives; for when a hypothesis is once posed, experiments are often done to ascertain if it is a good one, experiments which would never have been thought of without it.”
Moreover, Du Châtelet thought that experimental results could increase the probability of the hypothesis:
- “If it is found that these experiments confirm it, and that it not only explains the phenomenon that one had proposed to explain with it, but also that all the consequences drawn from it agree with observations, its probability grows to such a point that we cannot refuse our assent to it, and that is almost equivalent to a demonstration.”
However, Du Châtelet warned her readers that, when hypothesising, one must proceed with caution:
- “Without a doubt there are rules to follow and pitfalls to avoid in hypotheses. The first is, that it not be in contradiction with the principle of sufficient reason, nor with any principles that are the foundations of our knowledge. The second rule is to have certain knowledge of the facts that are within our reach, and to know all the circumstances attendant upon the phenomena we want to explain.”
Moreover:
- “Since hypotheses are only made in order to discover the truth, they must not be passed off as the truth itself, before one is able to give irrefutable proofs.”
So finally:
- “With this precaution one does not run the danger of taking for certain that which is not; and one inspires those who follow us to correct the faults in our hypotheses and to provide what they lack to make them certain.”
Du Châtelet greatly admired the British philosophers, Locke and Newton in particular. But her views on hypotheses have much more in common with her fellow Continental philosophers, Leibniz and Wolff.
*Translations are quoted from Du Châtelet, E. (2009), Selected Philosophical and Scientific Writings, J. P. Zinsser (ed.), I. Bour & J. P. Zinsser (trans.), University of Chicago Press.
Is Newton’s Explanation of Gravity a Hypothesis?
Kirsten Walsh writes…
In the General Scholium to Book 3 of Principia, Newton wrote:
- “Thus far I have explained the phenomena of the heavens and of our sea by the force of gravity, but I have not yet assigned a cause to gravity.”
He went on to explain that such a cause would be a hypothesis,
- “and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy.”
It might appear that Newton’s methodological statements don’t reflect his real attitude to causal explanations. He explained all the motions of bodies and the sea by the force of gravity. So in some sense, gravity was the cause of those motions. But if gravity was a cause, then wasn’t it a hypothesis? Was Newton’s famous statement “Hypotheses non fingo” a lie?
In this post, I’ll have a closer look at the role of causal explanations in Newton’s method of natural philosophy.
To begin, consider this statement from Query 28 of Opticks:
- “Whereas the main Business of natural Philosophy is to argue from Phaenomena without feigning Hypotheses, and to deduce Causes from Effects, till we come to the very first Cause, which certainly is not mechanical…”
Here, Newton outlined two central tasks for natural philosophers:
- To argue from phenomena without relying on, or giving credence to, hypotheses; and
- To infer causes from effects until you arrive at the first cause.
The first task is methodological, and it places a constraint on the kinds of inferences one may make from effect to cause. The second task is epistemological: it tells the philosopher what kind of knowledge to seek, and when to stop. Newton shed a little more light on this second task in Query 31:
- “By this way of Analysis we may proceed from Compounds to Ingredients, and from Motions to the Forces producing them; and in general, from Effects to their Causes, and from particular Causes to more general ones, till the Argument end in the most general.”
Perhaps recognising that, once constrained by task 1, task 2 would be too difficult for any single philosopher to complete, Newton wrote in Query 28:
- “And though every true Step made in this Philosophy brings us not immediately to the Knowledge of the first Cause, yet it brings us nearer to it, and on that account is to be highly valued.”
Furthermore, in Query 31, he writes:
- “And therefore I scruple not to propose the Principles of motion above-mention’d, they being of very general Extent, and leave their Causes to be found out.”
And so, in Principia, Newton inferred causes from effects as far as he was able to, while still following the advice of task 1. He stopped short of assigning a cause for gravity, because he could not deduce it from the phenomena. So as he wrote in the General Scholium of Principia:
- “It is enough [i.e. for the purposes of his argument] that gravity really exists and acts according to the laws that we have set forth and is sufficient to explain all the motions of the heavenly bodies and of our sea.”
To conclude, Newton doesn’t rail against causes per se, only against causes that cannot be proved by, or inferred from, experiment. I have argued that Newton was working with a clear distinction between theories and hypotheses, where a hypothesis is:
H1. Something that is, at best, only highly probable;
H2. A conjecture or speculation – something not based on empirical evidence; or
H3. A causal explanation – something concerning the nature of the phenomenon, rather than its physical properties.
I have changed the wording of H1 slightly from the definition I have given in previous posts. Now it looks like I might need to alter H3. What do you think?
Hypotheses versus Queries in Newton’s Opticks
Kirsten Walsh writes…
A while ago I argued that the queries in Newton’s early optical papers are not hypotheses. Rather, they are empirical questions that may be resolved by experiment. In Newton’s Opticks, however, his queries become increasingly speculative – especially the famous ‘Query 31’. What should we make of this? Did Newton abandon his early distinction between hypotheses and queries?
In his early optical papers, Newton explains that “the proper Method for inquiring after the properties of things is to deduce them from Experiments”. Having obtained a theory in this way, one should proceed as follows:
- specify queries that suggest experiments that will test the theory; and
- carry out those experiments.
He tells us that hypotheses have a role in this procedure. They may be useful for: (a) suggesting further experiments, as the first step toward specifying queries; and (b) ‘illustrating’ the theory to assist understanding.
The queries in Newton’s Opticks have been much talked about, and often Newton has been accused of slipping hypotheses into his work under the guise of the more-respectable query. To examine this claim, I looked at the draft manuscripts* of Newton’s Opticks; in particular, “The fourth book concerning the nature of light & ye power of bodies to refract & reflect it” (Add. 3970, 337-8).
The draft begins, as many of the other books of Opticks begin, with a list of observations, followed by numbered propositions. However, it contains little in the way of argument and virtually no discussion of experimental evidence. Shapiro points out that this is because this is a draft of an outline or plan of a book; not a draft of the book itself. The propositions are things that Newton hoped to prove. For example:
- Prop. 1. The refracting power of bodies in vacuo is proportional to their specific gravities.
Prop. 2. The refracting power of two contiguous bodies is the difference of their refracting powers in vacuo.
The draft contains a section entitled ‘The conclusion’, which contains five ‘hypotheses’. I am interested in ‘Hypothesis 2’:
- As all the great motions in the world depend upon a certain kind of force (wch in this earth we call gravity) whereby great bodies attract one another at great distances: so all the little motions in ye world depend upon certain kinds of forces whereby minute bodies attract or dispell one another at little distances.
- How the great bodies of ye earth Sun moon & Planets gravitate towards one another what are ye laws of & quantities of their gravitating forces at all distance from them & how all ye motions of those bodies are regulated by those their gravities I shewed in my Mathematical Principles of Philosophy to the satisfaction of my readers: And if Nature be most simple & fully consonant to her self she observes the same method in regulating the motions of smaller bodies wch she doth in regulating those of the greater… The truth of this Hypothesis I assert not because I cannot prove it. But I think it very probable because a great part of the phaenomena of nature do easily flow from it wch seem otherways inexplicable…
I. Bernard Cohen describes this as “a ‘whale’ of an hypothesis” – and he’s right! When Newton started writing out this statement, he intended for it to be ‘Proposition 18’. But at some point, he has scratched out ‘Prop 18’, and re-branded it as ‘Hypoth 2’. There is no real semantic difference between a proposition and a hypothesis, but, for Newton, there is an epistemic difference. Propositions are things that he is able to assert as true. Hypotheses are things that he is unable to assert, because he does not have the evidence. Newton clearly hoped to assert Proposition 18. But as he started to explicate it, he must have realised that he couldn’t prove it. Thus, he re-labelled it as a hypothesis.
When Newton abandoned the fourth book, and restructured the rest of his Opticks, this ‘Hypothesis 2’ appears to have been re-worked to become ‘Query 31’ in Opticks, 2nd edition (1717):
- Have not the small Particles of Bodies certain Powers, Virtues, or Forces, by which they act at a distance, not only upon the Rays of Light for reflecting, refracting, and inflecting them, but also upon one another for producing a great Part of the Phaenomena of Nature? For it’s well known, that Bodies act one upon another by the Attractions of Gravity, Magnetism, and Electricity; and these Instances shew the Tenor and Course of Nature, and make it not improbable but that there may be more attractive Powers than these. For Nature is very consonant and conformable to her self…
Here, there is an obvious semantic shift between hypothesis and query: the query is stated as a question. Some scholars have argued that this is the only difference between hypotheses and queries: in the Opticks, queries are simply Newton’s way of getting around his self-imposed ban on hypotheses. I claim that there is more to the shift than this. Newton is using the semantic structure of the query to explore a possible future research program. The epistemic difference between the query and the hypothesis is similar to the epistemic difference between Popper’s falsifiable and unfalsifiable theories. The former is testable-in-principle, whereas the latter is not; and testability is a necessary condition of something becoming well-tested.
There is a difference between Newton’s early queries and his later queries: the former are part of the process of justification; but the latter are part of the process of discovery. In a previous post I noted that:
- While Newton’s [early] method of queries is experimental, it does not appear to be strictly Baconian. For the Baconian-experimental philosopher, queries serve “to provoke and stimulate further inquiry”. Thus, for the Baconian-experimental philosopher, queries are part of the process of discovery. However, for Newton, queries serve to test the theory and to answer criticisms. Thus, they are part of the process of justification.
The queries in Newton’s later work seem closer to the Baconian tradition that inspired him.
That the themes of Hypothesis 2 and Query 31 appear in Rule 3 of Principia, raises questions about the status of Newton’s ‘Rules of Philosophising’ and how we should interpret the re-branding of ‘hypotheses’ as ‘rules’ in later editions of Principia. I’d love to hear what you think!
* Recently, Cambridge University put Newton’s papers online, making it possible for those of us who live ‘down under’ to examine copies of many of Newton’s manuscripts!
Hypotheses and Newton’s Rings
Kirsten Walsh writes…
In Ian Lawson’s recent post, he mentioned Hooke’s work on colours in thin films. In this post, I’ll look at how Newton used his hypotheses on light to build on Hooke’s work in some interesting and important ways.
In his optical work of the early 1670s, while Newton prefers theories to hypotheses, he thinks that hypotheses are acceptable, even useful, for two purposes:
- To ‘illustrate’ (i.e. provide an intuitively plausible explanation of) the theory; and
- To ‘suggest’ experiments.
However, he insists that hypotheses should always be removed from the final version of the theory. Recall Newton’s claim from his 1672 paper: “I shall not mingle conjectures with certainties”.
In December 1675, Newton wrote his paper, “An hypothesis explaining the Properties of Light”. Here, he published his hypotheses on the nature of light for the first time. To summarise them briefly:
- There is an ‘aethereal medium’;
- Aether vibrates, carrying sounds, smells and light;
- Aether penetrates and passes through the pores of solid substances;
- Light is neither the aether itself, nor the vibrations, but a substance that is propagated from ‘lucid’ bodies and travels through the aether;
- Light warms the aether and the aether refracts the light; and
- The rays (or bodies) of which light consists differ from one another physically.
In this paper, Newton claims that he is only discussing these hypotheses for the purposes of ‘illuminating’ his theory. Moreover, he does not assert that these hypotheses are true, and emphatically does not use them to support his theory. For example, when he discusses hypothesis (4), Newton is careful not to push too forcefully for any particular account of light. He says one might suppose light to be “an aggregate of various peripatetic qualities”, or “unimaginably small and swift” corpuscles of various sizes, or “any other corporeal emanation or impulse or motion of any other medium diffused through the body of the aether”:
- Onely whatever Light be, I would suppose, it consists of Successive rayes differing from one another in contingent circumstances, as bignes, forme or vigour… And further I would suppose it divers from the vibrations of the aether.
In this paper, there is a notable emphasis on experiment. For example, when Newton discusses hypothesis (1), he gives an account of a new electrical experiment which seems to support his claim. And when he discusses hypothesis (3), he discusses the implications for Boyle’s tadpole experiments. But the most important experiments in this paper are his investigations on the colours that appear between two glass surfaces.
Alan Shapiro notes that Newton began these investigations while he was reading Hooke’s Micrographia. But his experiments and mathematical descriptions quickly developed into something well beyond the scope of Hooke’s investigations. Hooke described the colours that appear when two thin sheets of glass are placed one on top of the other. When he made the thin film of air between the two sheets thicker or thinner by pressing the two sheets together with greater or lesser force, the colours changed. He observed that different colours appeared at different thicknesses, but he was unable to quantify this observation as he was unable to measure accurately the thickness of the film at any given point. Newton had the idea of placing a convex lens on top of a flat sheet of glass. This enabled him to easily calculate the thickness of the film of air, and the colours appeared as a set of concentric coloured circles centred at the point of contact between the two surfaces. These concentric circles are now known as ‘Newton’s Rings’.
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Opticks, Book 2, Figure 3
Next Newton considered his hypotheses. According to hypothesis (2) the vibrations of the aether vary in size, according to hypothesis (3) aether passes through the pores of solid substances, and according to hypothesis (6) rays of different colours will cause aethereal vibrations of different sizes. If these hypotheses were correct, he argued, then light of a particular colour would be reflected either when the length of the vibration, or some multiple of the length of the vibration, matched the thickness of the film, and transmitted otherwise. So he predicted that:
- if the Glasses in this posture be looked upon, there ought to appear at A [the centre], the contact of the Glasses, a black spott, & about that many concentric circles of light & darknesse, the squares of whose semidiameters are to sense in arithmetical progression.
Newton’s “Hypothesis” paper provides a good example of his method of hypotheses. He remains carefully detached from his own hypothesis, using it only to ‘illustrate’ his theory and to suggest further experiments. Newton was also careful to keep his hypotheses well separate from his theory; the paper ends with a series of ‘Observations’ that contain no reference to his hypotheses at all!
Hypotheses versus theories
Peter Anstey writes…
Chapter 5 of William Poole’s The World Makers (Peter Lang, 2010) opens with a very interesting epigraph from the Cambridge antiquarian Thomas Baker’s Reflections on Learning (1699):
- But we have been taught to distinguish betwixt Hypotheses and Theories, the latter of which are shrew’d things, as being built upon Observations in Nature, whereas hypotheses may be only Chymaeras: I should be glad to see that Theory, that is built upon such Observations … (p. 82)
While Poole doesn’t mention the connection, this distinction almost certainly derives from William Wotton’s precursor to Baker’s book, namely, Reflections upon Ancient and Modern Learning (London, 1694). There, Wotton claims:
- In judging of Modern Discoveries, one is nicely to distinguish between Hypothesis and Theory. (p. 235) … And therefore, that it may not be thought that I mistake every plausible Notion of a witty Philosopher for a new Discovery of Nature, I must desire that my former Distinction between Hypotheses and Theories may be remembered. I do not here reckon the several Hypotheses of Des Cartes, Gassendi, or Hobbes, as Acquisitions to real Knowledge, since they may only be Chimaera’s and amusing Notions, fit to entertain working Heads. I only alledge such Doctrines as are raised upon faithful Experiments, and nice Observations; and such Consequences as are the immediate Results of, and manifest Corollaries drawn from, these Experiments and Observations: Which is what is commonly meant by Theories. (p. 244)
This hypothesis–theory distinction seems to be of Wotton’s own making. It is an effective means of dealing with the problem of the utility of hypotheses in a climate in which the notion of hypothesis was, to say the least, on the nose. Wotton spouts the standard anti-hypothetical rhetoric – the hypotheses of Descartes and others are mere chimeras – but he is not insensitive to the fact that experiments and observations on their own are not sufficient for the advancing of true explanations.
Wotton was not an experimental philosopher. Rather, his Reflections was written as a defence of modern learning, and, in particular, the experimental philosophy, in the battle of the books. His comments and those of Baker, are therefore, indicative of the reach of the methodological stance of experimental philosophy beyond the writings of natural philosophers themselves.
Kant on experiments, hypotheses, and principles in natural philosophy
Alberto Vanzo writes…
As we have often noted on this blog, early modern experimental philosophers typically praised observations and experiments, while rejecting natural-philosophical hypotheses and assumptions not derived from experience. Along similar lines, Larry Laudan claimed that aversion to the method of hypothesis characterized “most scientists and epistemologists” from the 1720s to the end of the eighteenth century. Laudan mentioned Kant as one of the authors for whom “the method of hypothesis is fraught with difficulties”.
Immanuel Kant
In this post, I will sketch a different reading of Kant. I will suggest that Kant, alongisde other German thinkers like von Haller, is an exception to the anti-hypothetical trend of the eighteenth century. Kant held that natural philosophers should embrace experiments and observations, but they are also allowed to formulate hypotheses and to rely on certain non-empirical assumptions. They should develop fruitful relationships between experiments and observations on the one hand, (some) hypotheses and speculations on the other.
I will illustrate Kant’s position by commenting on a sentence from the Pragmatic Anthropology: when we perform experiments,
- we must always first presuppose something here (begin with a hypothesis) from which to begin our course of investigation, and this must come about as a result of principles. (Ak. 7:223)
1. “[W]e must always first presuppose something here (begin with a hypothesis)…”
“For to venture forth blindly, trusting good luck until one stumbles over a stone and finds a piece of ore and subsequently a lode as well, is indeed bad advice for inquiry”. Even if we tried to perform experiments in a theoretical void, our activity would still be influenced by hypotheses and expectations. “Every man who makes experiments first makes hypotheses, in that he believes that this or that experiment will have these consequences” (24:889).
Like British experimental philosophers, Kant acknowledges that hypotheses and preliminary judgements may be “mere chimeras” (24:888), “romances” (24:220), castles in the air, or “empty fictions” (24:746). Hypotheses, like castles in the air, are fictions, but not all fictions must be rejected. The power of imagination, kept “under the strict oversight of reason” (A770/B798), can give rise to useful “heuristic fictions” (24:262). What is important is to be ready to reject or modify our hypotheses in the light of experimental results, so as to get closer and closer to the truth.
2. “…and this must come about as a result of principles.”
What principles are involved in our natural-philosophical investigations? As is well known, Kant holds that nature is constrained by a set of principles that we can establish a priori, like the causal law. In what follows, I will focus on three other principles that guide our experimental activity. They are the principles of homogeneity, specification, and affinity.
- The principle of homogeneity states that “one should not multiply beginnings (principles) without necessity” (A652/B680). Kant takes it to mean that one must always search for higher genera for all the species that one knows. An example is the attempt to regard the distinction between acids and alkali “as merely a variety or varied expression of one and the same fundamental material” (A652-53/B680-81).
- The principle of specification prohibits one from assuming that there are lowest species, that is, species which cannot in turn have sub-species. This led, for instance, to the discovery “[t]hat there are absorbent earths of different species (chalky earths and muriatic earths)” (A657/B685).
- The principle of affinity derives from the combination of the principles of homogeneity and specification. It prompt us to look for intermediate specices between the species that we already know.
For Kant, the principles of homogeneity, specification, and affinity are not derived a posteriori from our experimental inquiries. They are a priori assumptions that guide them. We would not find higher genera, lower species, and intermediate species in the first place, unless we assumed that they exist and we tested that assumption with experiments and observations. For Kant, this is a non-empirical assumption that precedes and guides natural-philosophical inquiries. These do not unfold entirely a posteriori. They presuppose hypotheses and principles that are prior to experience and enable us to extend our knowledge of the world. Thus, rather than rejecting hypotheses and non-empirical assumptions as many experimental philosophers did, Kant holds that a guarded use of them is useful for our study of nature.
Von Haller on hypotheses in natural philosophy
Alberto Vanzo writes…
Typically, the experimental philosophers on whom we focus in this blog promoted experiments and observations, while decrying hypotheses and system-building. This is the case for several experimental physicians, to some of whom we have devoted the last two posts. Their Swiss colleague Albrecht von Haller thought otherwise. He published an apology of hypotheses and systems in 1751.
Von Haller was a novelist, a poet, and an exceptionaly prolific writer on nearly all aspects of human knowledge. He is said to have contributed twelve thousand articles to the Göttingische gelehrte Anzeigen. However, von Haller was mainly employed as an anatomist, physiologist, and naturalist. Like his Scottish colleague Monro I, he had studied in Leyden under Boerhaave. Having achieved Europe-wide fame for his physiological and botanical discoveries, von Haller was called by George II of England, prince-elector of Hanover, to occupy the inaugural chair of medicine, anatomy, botany and surgery at the newly founded University of Göttingen. Göttingen was under the strong influence of British culture throughout the eighteenth century and would later be the main centre of German experimental philosophers. While in Göttingen, von Haller was mainly engaged in his physiological and botanical studies, besides organizing an anatomical theatre, a botanical garden, and other similar institutions.
Haller’s essay, entitled “On the Usefulness of Hypotheses”, was first published as a premise to the German edition of Buffon’s Natural History. It was reprinted posthumously in 1787. Throughout these years, several authors in the German speaking-world endorsed Newton’s radically negative attitude towards hypotheses. For instance, few years after von Haller’s essay the physician Gerard van Swieten — also a pupil of Boerhaave — published a discourse on medicine in which he cried “may hypotheses be banned!”. And in the 1780s, when von Haller’s essay was being reprinted, the anthropologist Johann Karl Wezel proclaimed in broadly Newtonian spirit: “I only relate facts”.
Von Haller was aware of this anti-hypothetical fashion. He starts his essay by describing how naturalists had come to despise hypotheses. With the success of mathematical natural philosophy (the Newtonian form of experimental philosophy that had replaced Baconian natural histories), researchers started to rely (or at least, to claim that they were only relying) on what had been mathematically proven. This happened first in England with Newton, then in Holland with Boerhaave, then in Germany and France with Maupertuis and others.
For Haller, this was not a positive development. Peopled shifted from one excess, namely abusing of hypotheses, to an other, namely rejecting them altogether, while ignoring the virtuous middle way. Yet, while researchers were despising hypotheses, they were relying heavily on them:
- The great advantage of today’s higher mathematics, this dazzling art of measuring the unmeasurable, rests on a mere hypothesis. Newton, the destroyer of arbitrary opinions, was unable to avoid them completely. […] His universal matter, the medium of light, of sound, of the senses, of elasticity — was it not a hypothesis?
Von Haller makes other examples of natural-philosophical hypotheses, in order to highlight
- the true use of hypotheses. They are certainly not the truth, but they lead to it, and I say even more: humans have not found any way that is more successful in leading them to the truth [than hypotheses], and I cannot think of any inventor who did not make use of hypotheses.
What is this “true use of hypotheses”? It is their heuristic use. Hypotheses are claims to be tested by means of experiments and observations. Sets of hypotheses form large-scale systematic pictures that provide purpose and direction to our research. Think for instance of the heuristic value of the corpuscular hypothesis for the experimental activity of the early Royal Society (this is not von Haller’s example). Additionally, hypotheses make possible a public discussion of problems that scientists could not even mention if they were only allowed to talk about were facts, as some experimental philosophers hoped.
These experimental philosophers may reply to von Haller that they do not need to employ hypotheses to achieve those aims. All that is needed are queries. Von Haller would reply that queries are nothing else than hypotheses in disguise. “In fact, Hypotheses raise questions, whose answer we demand from experience, questions that we would not have raised if we did not formulate hypotheses”.
Von Haller was not the only author in the German-speaking world to provide a qualified defense of hypotheses. Christian Wolff before him and Immanuel Kant after him made similar points. However, von Haller was much more engaged in empirical research than either of them. His work seems to me to have been very much in the spirit of experimental philosophy. Finding such an explicit and detailed defense of hypotheses by such an author reminds us that the methodological views of early modern experimentalists were not monolithic and that, even in a strongly anti-hypothetical age, some authors were aware of the benefits of a careful use of hypotheses in the study of nature.
Newton’s Method in Three Minutes
Kirsten Walsh writes…
Last week I competed in the Otago University Three-Minute Thesis Competition. I had to explain my PhD thesis in no longer than three minutes. It was challenging indeed, in such a short length of time, to describe my research, communicate its significance and impart my enthusiasm for it – while pitching it at the level of an intelligent non-expert. Fortunately, I had great material to work with. There are so many interesting stories about Newton! Unfortunately, it’s often difficult to figure out which stories are true.
I opted to begin with the ‘approximately true’ story of Newton’s anni mirabilis, or miraculous years. The general thrust of the story is true, even if some of the particulars are false: the plague years mark a significant turning point in Newton’s scientific work. As Whiteside pointed out over forty years ago, we may
- “salute this first creative outburst – whether or not contained in one single marvelous year – of a man who twenty years afterwards was to construct a scientific Weltanschauung which is, in its essentials, still ours.”
So, with apologies to those of you with ‘historically sensitive’ ears, here is my script for the three-minute thesis competition:
It’s 1665. Cambridge has been struck by Plague, and Newton has been sent home from University. Summer is stretching out before him. Nice! What will he do on his extended summer holiday? Well, he did what I imagine most Scarifies* do on their summer holidays: he invented calculus, discovered the composition of light, and (after watching an apple fall from a tree) conceived the laws of universal gravitation… Okay, so perhaps Newton wasn’t quite your typical undergraduate student. The story about the apple is controversial, but everyone agrees about the discoveries. Scholars have called those years the ‘years of miracles’.
Why were they ‘miraculous’? Well, these were revolutionary discoveries – and there were so many of them. They provided the basic material for Newton’s Principia, and his Opticks. Enough material for a lifetime of publications! And real publications. Not just those ‘puff pieces’ that fill our journals nowadays. All in just 2 years!
Furthermore, these discoveries seemed to come out of nowhere. Newton was able to invent, discover and conceive things no one else could, because seemingly he had invented an entirely new scientific method. He had come up with a whole new way of mathematising physics, and claimed to have achieved mathematical certainty! Philosophers and scientists tried to emulate his method. But no one was as successful as Newton. Whatever Newton was doing, he was doing it right. But what was he doing?
This is the central question of my PhD, and it’s a question that dominates discussions of scientific method even now, 300 years later. But scholars still barely understand what Newton’s method was. Did Newton really think his scientific theories were as certain as mathematical proofs? Why did he think his theory of gravity was true, when he couldn’t even say for certain what gravity is? And, at the centre of it all, the question that’s been keeping me up at nights (as it has kept up generations of Newton-scholars before me): what did Newton mean when he wrote that enigmatic sentence at the end of Principia: ‘Hypotheses non fingo’; ‘I do not feign hypotheses’?
I do not feign hypotheses. What an odd thing to say. What does it even mean? ‘I haven’t invented these hypotheses’? ‘I didn’t prove them’? This sentence lies at the heart of my thesis. Unlike other Newton scholars, I think it describes a crucial aspect of Newton’s method. What it tells us is that Newton made a distinction. On the one hand, theories: mathematical, certain, experimentally confirmed. On the other hand, hypotheses: non-mathematical, uncertain, non-experimental, and speculative. This distinction is a crucial feature of Newton’s spectacularly successful scientific method. And I think it’s this distinction that explains Newton’s years of miracles.
The idea of anni mirabiles seems closely-related to the notion of a scientific revolution, which has been much discussed since Kuhn published The Structure of Scientific Revolutions in 1962. Philosophers of science disagree philosophically over the importance of revolutions to science, and historically over the occurrence of any genuine scientific revolutions. However, it is interesting to note that historians have recognised several anni mirabiles in the history of science. For example, 1543, the year that Vesalius published De Humani Corporis Fabrica and Copernicus published De Revolutionibus Orbium Coelestium. And 1905, the year that Einstein published his three ground-breaking papers in the Annalen der Physik. What role have these anni mirabiles played in the history of science? What do they tell us about scientific progress? Norwood R Hanson once said:
- “It is possible both to be driven by intuition and at the same time to reason carefully. Most scientific discoveries, indeed, result from just such an intertwining of headwork and guesswork.”
What do you think?
*Otago Undergraduate Students
