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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 Newton’s Epistemic Triad

Kirsten Walsh writes…

Over the weekend, I participated in a conference on ‘Newton and his Reception’, at Ghent University.  I presented a paper based on my idea that Newton is working with an ‘epistemic triad’.  I had an excellent audience in Ghent, and received some very helpful feedback, but I’d like to hear what you think…

To begin, what is Newton’s ‘epistemic triad’?

In his published work, Newton often makes statements about his purported method in order to justify his scientific claims.  In these methodological statements, he contrasts things that have strong epistemic credentials with things that lack those credentials.  Consider, for example, these passages from his early papers on optics:

    For what I shall tell concerning them is not an Hypothesis but most rigid consequence, not conjectured by barely inferring ’tis thus because not otherwise or because it satisfies all Phænomena … but evinced by ye mediation of experiments concluding directly & wthout any suspicion of doubt. (6 February 1672)
    I shall not mingle conjectures with certainties… (6 February 1672)
    To determine by experiments these & such like Queries wch involve the propounded Theory seems the most proper & direct way to a conclusion. (3 April 1673)

What these passages tell us is that Newton is making a distinction between theories, which are certain and experimentally confirmed, hypotheses, which are uncertain and speculative, and queries, which are not certain, but provide the proper means to establish the certainty of theories.  I call this three-way division Newton’s ‘epistemic triad’, and argue that this triad provides the framework for Newton’s methodology.

To support this argument, I defended the following three theses:

Endurance thesis.  There are some general features of Newton’s methodology that don’t change.  These are characterised by the framework of the epistemic triad.

Developmental thesis. There are some particular features of Newton’s methodology that change over time.  These can be characterised as a development of the epistemic triad.

Contextual thesis. There are some particular features of Newton’s methodology that vary with respect to context (namely, mechanics versus optics).  These can be characterised as an adaptation of the epistemic triad to particular contexts.

The developmental and contextual theses are not news to most Newton scholars.  It is commonly accepted that Newton’s methodology changed in important ways over the course of his life, and that there are methodological differences between Principia and Opticks.  The endurance thesis is more problematic, so I made a special effort to show that Newton’s use of hypotheses is more consistent than we think.  I argued that:

  1. In Principia, Newton appears to be working with the same implicit definition of ‘hypothesis’ that he works with in his early optical papers; and
  2. Hypotheses perform similar methodological roles in all of Newton’s natural philosophical work.

I need to do some more work to properly explicate this methodological role.  But, to state it very broadly, Newton temporarily assumes hypotheses, which act as ‘helping premises’ in his inferences from phenomena.  The fact that a statement may appear in Newton’s writing as a hypothesis, and then reappear later in a query, rule of reasoning, or phenomenon, has convinced many Newton scholars that Newton is inconsistent in his use of hypotheses. Against this conviction, I argue that Newton applies the label ‘hypothesis’ to things that perform a particular function, rather than to a particular claim.

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:

  1. specify queries that suggest experiments that will test the theory; and
  2. 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!

Newton’s Early Queries are not Hypotheses

Kirsten Walsh writes…

In an earlier post I demonstrated that, in his early optical papers, Newton is working with a clear distinction between theory and hypothesis.  Newton takes a strong anti-hypothetical stance, giving theories higher epistemic status than hypotheses.  Newton’s corpuscular hypothesis appears to challenge his commitment to this anti-hypothetical position.  Today I will discuss a second challenge to this anti-hypotheticalism: Newton’s use of queries.

Newton’s queries have often been interpreted as hypotheses-in-disguise.  But in his early optical papers, Newton’s queries are not hypotheses.  In fact, he is building on the method of queries prescribed by Francis Bacon, for whom assembling queries is a specific step in the acquisition and development of natural philosophical knowledge.

To begin, what is Newton’s method of queries?  In a letter to Oldenburg, 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: (1) specify queries that suggest experiments that will test the theory; and (2) carry out those experiments.

He then lists eight queries relating to his theory of light and colours, e.g.:

    “4. Whether the colour of any sort of rays apart may be changed by refraction?
    “5. Whether colours by coalescing do really change one another to produce a new colour, or produce it by mixing onely?”

He ends the letter, saying:

    “To determin by experiments these & such like Queries which involve the propounded Theory seemes the most proper & direct way to a conclusion.  And therefore I could wish all objections were suspended, taken from Hypotheses or any other Heads than these two; Of showing the insufficiency of experiments to determin these Queries or prove any other parts of my Theory, by assigning the flaws & defects in my Conclusions drawn from them; Or of producing other Experiments which directly contradict me, if any such may seem to occur.  For if the Experiments, which I urge be defective it cannot be difficult to show the defects, but if valid, then by proving the Theory they must render all other Objections invalid.”

While Newton’s 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.

Newton uses queries to identify points of difference between his theory and its opponents.  For example, in a letter to Hooke he writes:

    “I shall now in the last place proceed to abstract the difficulties involved in Mr Hooks discourse, & without having regard to any Hypothesis consider them in general termes.  And they may be reduced to these three Queries.  [1] Whether the unequal refractions made without respect to any inequality of incidence, be caused by the different refrangibility of several rays, or by the splitting breaking or dissipating the same ray into diverging parts; [2] Whether there be more then two sorts of colours; & [3] whether whitenesse be a mixture of all colours.”

And in a letter to Huygens, Newton says:

    “Meane time since M. Hu[y]gens seems to allow that white is a composition of two colours at least if not of more; give me leave to rejoyn these Quæres.
    “1. Whether the whiteness of the suns light be compounded of the like colours?
    “2. Whether the colours that emerg by refracting that light be those component colours separated by the different refrangibility of the rays in which they inhere?”

In both cases, Newton is using queries to steer the debate towards claims that can be tested and resolved by experiment.  On both occasions, Newton devotes a considerable amount of space to discussing the experiments that might determine these queries.

These early queries are not hypotheses.  Rather, they are empirical questions that may be resolved by experiment.  This is not merely a matter of semantics. In the same letter to Hooke, Newton demonstrates this by distinguishing between philosophical queries and hypothetical queries.  A philosophical query is one that can be determined by experiment, a hypothetical query cannot.  Newton argues that philosophical queries are the only acceptable queries.  He equates hypothetical queries with begging the question.

In his later work, Newton’s queries become increasingly speculative, suggesting that they function as de facto hypotheses.  Does Newton ultimately reject his early ‘method of queries’?

Next Monday we’ll have a guest post from Greg Dawes on Galileo and the Experimental Philosophy.

Does Newton feign an hypothesis?

Kirsten Walsh writes…

Newton’s famous pronouncement, Hypotheses non fingo, first appeared in 1713, but Newton’s anti-hypothetical stance is present as early as 1672, in his first papers on optics.  In his first publication, he introduces his notion of certainty, and insists that his doctine of colours is a theory; not an hypothesis:

    For what I shall tell concerning [colours] is not an Hypothesis but most rigid consequence… evinced by ye mediation of experiments concluding directly & without any suspicion of doubt.

Despite these clear anti-hypothetical themes, a corpuscular hypothesis lies beneath Newton’s theory of light and colours.  What are we to make of this?  Is Newton guilty of feigning an hypothesis? Is Wolff correct when he says that Newton “indulges in hypotheses in those very areas in which they think he abstained from employing them“?

To begin, what does Newton mean by Hypotheses non fingo?  ‘Fingo’ has been variously translated as ‘frame’, ‘make’, ‘imagine’ and ‘devise’. Experts argue that ‘feign’ is the most appropriate translation.  While it has a variety of meanings, such as to form, to invent, to forge, or to suppose erroneously, the word ‘feign’ also carries the nuance of pretence, counterfeit, or sham.  Thus, they argue that while Newton indeed conceived or framed hypotheses, he did not attach any special epistemic status to them.  He maintained a clear demarcation between theories that were supported by experimental results and hypotheses that were merely unsupported speculations.

Now let’s take a closer look at Newton’s early optical papers.  Newton claims that his doctrine of colours is a theory, not an hypothesis, for three reasons:

  1. It is certainly true, because it is supported by (or deduced from) experiment;
  2. It concerns the physical properties of light, rather than the nature of light; and
  3. It has testable consequences.

These are the three key aspects of Newton’s early methodology.  He refers to them again and again throughout the debate that followed the publication of his first optical paper.

Newton explicates his corpuscularian view in his first optical paper and describes light rays as substantial bodies.  But when his opponents accuse him of hypothesising, Newton argues that he is not guilty.  Firstly he argues that this hypothesis is not necessary for his explanation of colours.  Secondly he argues that he attaches no special epistemic merit to his hypothesis because:

  1. It is not supported by experiment;
  2. It concerns the nature of light; and
  3. It has no testable consequences.

While Newton never gives up his corpuscularian view, he attempts to explicate and promote his theory without referring to it.  He argues that he doesn’t need to provide any hypothesis on the nature of light – his theory on the properties of light is sufficient on its own.

I claim that Newton isn’t guilty of violating his anti-hypothetical stance.  He demonstrates that he can distinguish between theory and hypothesis, giving the former higher epistemic status than the latter.  He does not pretend to have empirical support for his corpuscular hypothesis, nor does he try to ‘prop it up’ on other grounds.  Perhaps he regrets having ever opened the proverbial can of worms, for the next time he explicates his theory of light and colours, he does so without any reference to the corpuscular hypothesis or the nature of light.

That Newton can tell the difference between good scientific explanations and speculations is further supported by his use of queries in these early optical papers, but more on this next time.  To conclude,  I think Newton is not guilty of feigning an hypothesis.  What do you think?