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A Historical Introduction to the
Philosophy of Science

Ch. 7: The Seventeenth-Century Attack on Aristotelian Philosophy

Book cover: A Historical Introduction to the Philosophy of Science by John Losee

The following is a summary of the seventh chapter of John Losee's book, A Historical Introduction to the Philosophy of Science (fourth edition), with some ancillary notes.

Philosophers discussed in this chapter: Galileo Galilei (1564–1642); Francis Bacon (1561–1626); René Descartes (1596–1650)

I. Galileo

[p. 46] Galileo made many telescopic observations of astronomical objects that questioned the Church's Aristotelian world-view (e.g., sunspots, Earth's moon, Jupiter's moon).

The preface and conclusion to his The Dialogue Concerning the Two Chief World Systems (1632) treated the Ptolemaic and Copernican systems as merely mathematical instruments, while the remainder argued for the reality of the Copernican system.

[pp. 46–7] After Galileo recanted before the Inquisition, his Dialogues Concerning Two New Sciences (1638) demonstrated the failure of Aristotle's physics.

[p. 47] As a Pythagorean, Galileo identified only mathematical properties of matter as 'primary qualities':

  • shape
  • size
  • number
  • position
  • 'quantity of motion'

Secondary qualities (colours, tastes, odours, sounds) exist only in the mind of the perceiver.

Galileo demarcated science from non-science by excluding from science:

  • Aristotelian teleological 'explanations' (e.g., 'natural motion')
  • secondary qualities

[pp. 47–8] Galileo replaced Aristotle's qualitatively described spaces (centre of universe, sub-lunar, celestial) with a quantitative system of coordinates. Contradictorily, he also argued that celestial bodies (including the Earth) move naturally in perfect circles.

[p. 48] Galileo agreed with Aristotle's two-stage inductive–deductive method going from observations to general principles and back to observations.

[p. 49] But he criticized Aristotelians who ignored observations by starting with first principles, holding back scientific progress (e.g., sunspots, immutability).

Galileo deduced motions of falling bodies and real pendulums by first conceptualizing them as idealized bodies. Two examples are:

  1. free fall in a vacuum extrapolated from bodies falling through fluids of decreasing density
  2. ideal pendulum idealized as hanging from a 'mass-less' string with no air resistance

Galileo emphasized this importance of creative imagination, over and above induction by simple enumeration and the methods of agreement and difference.

Galileo exemplified Grosseteste's and Roger Bacon's advice by deducing from his hypothesis about projectile motion two observational facts that were not used to construct his theory:

  1. maximum projectile range is 45 degrees [postdiction]
  2. equal projectile range is achieved from angles equidistant from 45 degrees [prediction]
Book cover: Enlightenment Now: The Case for Reason, Science, Humanism, and Progress by Steven Pinker

Such successful novel deductions constitute strong confirmation of the theory and genuine scientific explanation.
[LA: For more on the requirement that the observational evidence be independent of theory construction, see Sec. 4 of my 'Towards an Objective Theory of Rationality'.]

[p. 50] Galileo, however, was ambivalent about the need for further testing of a hypothesis beyond the initial confirmation (contra Grosseteste and Roger Bacon).

[pp. 50–1] Despite his expressed ambivalence, Galileo is credited with performing many experiments on falling bodies, floating bodies and observations of stars (e.g., using inclined planes and pendulums).

[pp. 51–2] On the other hand, early on, Galileo dismissed experimental evidences that did not confirm his theory of:

  • the relationship between velocity of fall and density, and
  • the timing and frequency of tides

He dismissed the counter-evidences as due to 'unnatural accidents' and 'secondary causes' [LA: known as 'ad hoc hypotheses'].

[p. 53] Galileo's dual legacy is his actual working examples of:

  1. novel mathematical deduction as explaining physical phenomena, and
  2. abstracting from material phenomena to construct idealized entities

Questions to Consider:

  1. What do you think of the distinction between primary (mathematical) qualities and secondary (phenomenal) qualities? Is it useful? Is it real?
  2. Did Galileo do away completely with Aristotle's notion of 'natural motion'?
  3. How important are idealised models of natural systems to scientific explanation?
  4. How should a scientist proceed when an experimental result conflicts with their hypothesis?

II. Francis Bacon

Book cover: What Is This Thing Called Science? by Alan F. Chalmers

[p. 55] In 1620, Francis Bacon published his Novum Organum, the formulation of a new scientific method to replace the Aristotelian approach (Organon: compilation of Aristotle's writings). The publication of Bacon's, New Atlantis (1627) prefigured the modern scientific enterprise as a collective activity of a community of scientists.

Bacon's legacy as a champion and innovator in scientific method is disputed. The disputants agree that:

  1. Bacon offered no concrete examples of his new method
  2. Bacon's literary ability led many scholars to see him as a leading figure in the scientific revolution
  3. Bacon's originality, if any, is his theory of scientific method

[p. 56] In Novum Organum, Bacon identified four prejudices ('Idols') that distort perception of nature:

  1. Idols of the Tribe: innate tendency to hasty generalization and overemphasize confirmations
  2. Idols of the Cave: learned biases
  3. Idols of the Market-Place: tendency to use common meanings of words that impede concept-formation
  4. Idols of the Theatre: received philosophical dogmas and methods (e.g., Aristotle's principles)

Bacon accepted Aristotle's inductive–deductive loop from observations to general principles and back to observations and saw science as a practical enterprise.

[pp. 56–7] Bacon criticized the Aristotelians' use of the inductive phase for:

  1. foregoing systematic experimentation/instrumentation for haphazard data collection
  2. generalizing too hastily, leaping to too general first principles
  3. relying on induction by simple enumeration and ignoring negative instances

[p. 57] Bacon criticized the Aristotelians' use of the deductive phase for:

  1. failing to define precisely the terms used in the deductive syllogisms
  2. providing inadequate inductive support for the first principles

Bacon failed to distinguish Aristotle's procedure that emphasized the arriving at first principles by observation and induction from that of later pseudo-Aristotelians who short-circuited the procedure by starting with first principles.

[p. 58] Bacon's 'new' method of science featured a pyramid of increasingly general inductive correlations ('Ladder of Axioms') and a method of excluding accidental correlations ('Method of Exclusion').

At the base of the pyramid, the scientist collects observational facts. Next, the scientist looks for correlations of increasing generality ('Ladder of Axioms').

The scientist excludes accidental correlations by inspecting Tables of Presence, Absence, and Degrees ('Method of Exclusion').

[p. 59] This 'Method of Exclusion' is superior to Aristotle's induction by simple enumeration for its ability to isolate accidental correlations from essential via the scientist looking for absences and relative intensities of correlations.

For Bacon, 'Prerogative Instances' of correlations are especially suited to identifying essential correlations. One such 'Prerogative Instance' is the 'Instance of the Fingerpost': a 'crucial' observation is used to decide between competing explanatory hypotheses. The hypothesis that entails the 'crucial' observation wins out against all the other hypotheses that entail the opposite of the observation (e.g., observing non-opposing tides on opposite coasts falsifies the 'basin hypothesis' of tides).
[LA: This method prefigured the later notion of a single 'crucial experiment' deciding between competing hypotheses.]

Book cover: The Invention of Science: A New History of the Scientific Revolution by David Wootton

Bacon overemphasized the significance of a 'crucial' observation in deciding between hypotheses as there may be other unknown explanatory hypotheses that are also in agreement with the observation [LA: known later as the 'Duhem–Quine Underdetermination Thesis'].

Bacon's 'Instance of the Fingerpost' is not new as this deductive method of eliminating hypotheses had antecedents in the ideas of Aristotle, Grosseteste and Roger Bacon.

[pp. 59–60] At the apex of Bacon's induction pyramid were the metaphysical general principles he named 'Forms'. These are irreducible qualities ('simple natures') that occur in various combinations to produce effects (much like Aristotle's material and efficient causes)—not to be confused with Platonic forms or Aristotle's formal causes.
[LA: For more on Aristotle's four causes, see https://en.wikipedia.org/wiki/Four_causes]

[p. 60] Bacon thought of Forms in atomistic terms, but rejected the atomist attribution of impact and impenetrability to atoms and the idea of a continuous void. He did attribute 'forces' and 'sympathies' to atoms.

For Bacon, propositions describing Forms are universally true and the converse also true (e.g., 'heat' is identical to a 'rapid expansive motion of small particles'; thus, when heat is present, so is this rapid expansive motion, and conversely so).
[LA: This deducibility of statements about micro-particles from statements about phenomena is a precursor to the later-known 'reductionist' view of scientific explanation.]

In some places, Bacon spoke of 'Forms' as physical 'laws'. But unlike our modern notion of a 'physical law', Bacon's conception of a 'law' remained distinctly Aristotelian in that for Bacon, physical laws:

  1. are decreed by a power, as with civil laws
  2. are not expressed by mathematical relations
  3. express the relations between substances with properties and powers

[p. 61] In contrast to Aristotle who saw knowledge of nature as an end in itself, for Bacon, the goal of scientific discovery is to gain power over nature for the betterment of humankind. Bacon objected morally to Aristotle's passivity and to the Aristotelians' resistance to progress.

[p. 62] In the pursuit of such progress, Bacon advocated for the funding of cooperative scientific projects. His vision was only realized generations later with the founding of the Royal Society.

Bacon also forced the separation between scientific enquiry and teleology/natural theology. For Bacon, disputes about final causes of natural phenomena only impedes scientific and human progress.

Questions to Consider:

  1. How would you contrast Galileo's approach to scientific method with Francis Bacon's?
  2. How useful is Francis Bacon's four classes of Idols' in minimizing psychological and perceptual biases?
  3. Is it possible, or even desirable, to eliminate all biases when making scientific observations?
  4. Can a single 'crucial' observation ever decisively eliminate a competing theory?
  5. What are the similarities and differences between Francis Bacon's notion of 'Forms' and the contemporary scientific understanding of physical laws and forces?
  6. Do you agree with Francis Bacon that the scientific enterprise has the moral purpose of improving human lives?

III. Descartes

Book cover: Meditations and Other Metaphysical Writings by Rene Descartes

[p. 63] After laying the foundations of analytic geometry (1618), Descartes had a dream in which he was called by the Spirit of Truth to reconstruct human knowledge on incorrigible foundations (similar to mathematics).

In various publications, Descartes argued for a mechanistic view of nature centred on impact and pressure of constituent particles.

[p. 64] Descartes inverted the procedure of enquiry in Francis Bacon's pyramid of knowledge by placing certainly known first principles as the first step [see diagram on p. 69].

Through Descartes method of doubt, he concluded the certainty of his own existence and the existence of a Perfect Being. Such a perfect being would not systematically deceive humans about the world external to the mind.

Descartes' criteria for certainty was that an idea be:

  1. clear – immediately present to the mind (e.g., idea of 'bentness' of a stick partially immersed in water), and
  2. distinct – both clear and unconditioned (e.g., understand law of refraction that applies to case of 'bentness' of a stick)

[p. 65] Examining the changing attributes of a melting lump of wax, Descartes concludes the real and only 'essence' of the wax is its extension. This knowledge about the essence of material bodies is an intuition of the mind.

Descartes followed Galileo in contrasting the 'primary quality' of extension with the subjective 'secondary qualities' (colours, sounds, tastes, odours).

While rejecting the possibility of a vacuum as a contradiction in terms, Descartes accepted classical atomism and restricted scientific enquiry to what can be described mathematically. Here, he synthesised the Archimedean, Pythagorean and atomist points of view.

[p. 66] Descartes equivocated on his meaning of 'extension' between 'being filled by matter' [p. 65] and meaning a relationship a body has to other bodies. His conception of 'extension', then, was not clear and distinct (a major problem for his physics).

[pp. 66–7] From Descartes' understanding of extension, he derived three important a priori physical principles:

  1. all motion is caused by impact or pressure (denying occult action-at-a-distance, such as magnetic and gravitational forces)
  2. all motion is a cyclical rearrangement of bodies in a closed loop (as there is no vacuum) [p. 67]
  3. motion is conserved perpetually (as God would not let the universe run down)

[p. 67] From this principle of conservation of motion, Descartes derived three subsidiary laws of motion about inertia (Law I), natural motion in a straight line (Law II) and conservation of motion on impact (Law III (A)/Law III (B)).
[LA: As modern as these laws are, Descartes conservation of motion laws were later superseded by the law of conservation of energy.]

From these three laws, Descartes further derived seven rules of impact for specific kinds of collisions. These laws turned out to be mistaken as Descartes took size to be a determining factor and not weight.

[p. 68] Descartes system of deduction from first principles is wide in scope (shown on p. 69].

Book cover: Key Philosophical Writings by Rene Descartes

Although wide in scope, knowledge of first principles is limited in application as the same principles apply to an indefinitely many circumstances. As Descartes conceded to Francis Bacon, the scientist must still seek correlations among discrete phenomena (e.g., knowledge of anatomical structure for deductions in physiology).

[p. 69] A second role for observation for Descartes was suggesting hypotheses about mechanisms, usually employing an analogy with everyday experience (e.g., motions of planets analogous to bits of cork in a whirlpool).

[p. 70] Sometimes Descartes' analogies led him to ignore existing evidence (e.g., he ignored Harvey's evidence that the heart contracts with each pulse).

Descartes recognized that an observation may be deduced from more than one set of explanatory premises (consisting of laws of nature plus circumstances plus hypothesis). He specified that other observations be found that are deduced from one hypothesis but not the others. Descartes often did not follow his own advice, seeing experimentation as useful in formulating a hypothesis while ignoring their use in verifying a hypothesis.

[p. 71] Descartes gave due weight to the need for certainty and to the complexity of phenomena.

Malebranche saved Descartes principle of the preservation of 'quantity of motion' by interpreting it as 'momentum'. Descartes' general laws can only explain phenomena when used in conjunction with discrete facts and lower-level hypotheses. In that way, discrepancies between Descartes general laws and observation can always be fixed by modifying the lower-level hypotheses while leaving Descartes' principles intact. That flexibility guaranteed the use of Descartes' system into the next century.

Questions to Consider:

  1. Can a priori reasoning alone validate first principles in science?
  2. Is Descartes' inversion of the procedure of enquiry an improvement on Francis Bacon's pyramid of knowledge?
  3. Do scientists need God to guarantee the reliability of our perceptions of the external world?
  4. How important are analogies in science for building theories? If they are important, what role do they play?
  5. Is the fact that a general law can always be saved from falsification by a modification of a lower-level hypothesis detrimental to the notion of objective scientific knowledge?

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