Transcript Document 7351268

History and Philosophy
of Science
Lecture 2
History and Philosophy of Science
The history and philosophy of science can inform our research in
science informatics by providing
• theories of explanation and scientific knowledge;
• views of discovery and justification in the sciences;
• perspectives on scientific progress and the distinction
between normal and revolutionary science;
• narratives that reflect actual scientific practice and needs; and
• case studies to inspire novel informatics capabilities.
As a result, a foundation in history and philosophy can lead us
toward general informatics solutions as opposed to systems that
address ad hoc, problem-specific scenarios.
The Concerns of the Philosophy of Science
Philosophy of science is a broad discipline that investigates the
concepts, activities, and interaction of scientists, including
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the structure of scientific explanations;
the form of scientific methodology;
the methodology of scientific justification;
the context of scientific discovery; and
the nature of scientific progress.
Although other topics also arise, the listed ones are the most
relevant to science informatics.
Scientific Explanation
Scientific explanations emphasize the reasons why an event
happened rather than a description of the event itself.
In practice, scientific explanations combine situation specific
conditions with general principles expressed as
• logical sentences;
• mathematical equations;
• qualitative graphic or linguistic accounts;
• computer programs; and other forms.
Much of this work began with Carl Hempel and Paul
Oppenheim’s Studies in the Logic of Explanation from 1948.
Deductive-Nomological Explanation
This view treats scientific explanations as deductive arguments
where initial conditions and general laws imply observations.
C1, C2, ..., Cm Statement of antecedent conditions
Logical
Deduction
L1, L2, ..., Ln Statement of general laws
-------------------E Description of the empirical
phenomenon to be explained.
Schema taken from Hempel and Oppenheim’s 1948 paper.
Deductive Reasoning
Logical deduction is often characterized by modus ponens:
If P, Then Q
P
-------------------Q
Mapping to the DN view of explanation,
“If P, then Q” == general laws
“P” == the set of antecedent conditions
“Q” == the event to be explained.
Laws may be expressed in other formalisms (e.g., mathematical
equations), but there must be a mechanism to infer their
consequences from observations.
Hypothetico-Deductive Method
Popularized by William Whewell in the 1800s, this view of the
scientific method consists of two stages of activity.
Discovery refers to those processes that lead to the statement of
a conjecture based on observations.
Justification concerns the evaluation and acceptance of scientific
knowledge once stated.
Whewell posited three conditions for justification:
1. The hypothesis must predict unseen phenomena of the type
that it was meant to explain.
2. The hypothesis must help explain phenomena of a new type.
3. The hypothesis must fit within a theory that becomes more
coherent (unified, simple, etc.) over time.
Karl Popper and Falsification
A focus on confirmation raises Hume’s problem of induction.
That is, past evidence may not be indicative of future events.
Popper suggests a focus on falsification where scientists seek to
refute their hypotheses through experiment.
Falsificationism posits that one cannot prove theories or
hypotheses true, or even probable.
Under this view, hypotheses are either false or corroborated.
Popper’s philosophy required the sciences to establish falsifiable
hypotheses—anything else is pseudoscience.
Scientific Discovery
Philosophers largely ignored scientific discovery, believing it to
be immune to logical or heuristic analysis. Popper wrote:
The initial stage, the act of conceiving or inventing a theory, seems
to me neither to call for logical analysis nor to be susceptible of it.
The question how it happens that a new idea occurs to a
man…may be of great interest to empirical psychology; but it is
irrelevant to the logical analysis of scientific knowledge…My view
may be expressed by saying that every discovery contains an
‘irrational element’, or ‘a creative intuition’…
Popper was not alone in his views. Hempel among others
believed in the irrationality of discovery.
In the latter part of the 20th century, philosophers, psychologists,
and a new breed, artificial intelligence researchers, posited
induction and abduction as a means to mechanize discovery.
Inductive Reasoning
Inductive reasoning identifies specific commonalities across
several events and posits a corresponding general claim.
Q1 is P
Q2 is P
…
Qm is P
-------------------All Q’s are P
Evidence
Claim
The claim is not justified logically and is at best supported
statistically. Some consider induction useful only for evaluation.
Abductive Reasoning
Abductive reasoning involves explaining an event by positing a
statement that, if true, would manifest that event.
If P, Then Q
Q
-------------------P
Theory
Event
Hypothesis
In the schema above, we observe event Q and we know that if
some hypothesis P were true, we could explain Q, so we infer P.
Charles Peirce discussed abduction in detail and claimed that it
was the sole source of new ideas in science.
Scientific Progress: Kuhn
Thomas Kuhn distinguished between two types of science.
Normal science involved puzzle solving activity that revolved
around some current scientific theory.
Revolutionary science arose when anomalies overwhelmed the
prevailing theory and scientists searched for a new paradigm.
Notably Kuhn believed that each new paradigm signifies
progress by increasing in scope and, in particular, by
• explaining most of the anomalies driving the paradigm shift
• accounting for most of the phenomena covered by the old
paradigm
Scientific Progress: Lakatos
Imre Lakatos posited two types of knowledge in a theory:
The hard core consisted of those ideas central to a research
programme that one refuses to refute based on observation.
The protective belt of auxiliary hypotheses that may be modified
in the face of anomalies.
For Lakatos, a research programme is more permanent than a
theory since it is tied to the core while the belt may change.
Anomalies do not drive the revision of research programmes.
Instead, science progresses to new programmes when
• the current programme no longer produces new ideas
• the new programme explains the success of the current one
and has greater explanatory power.
History of Science
The history of science is an empirical field that investigates
• the methodological practices,
• the personal characteristics, and
• the social pressures
that contribute to scientific activity.
Thomas Kuhn wrote, “historical study [can] yield a new sort of
understanding of the structure and function of scientific research.”
More specifically, the history of science can identify the role of
• scientific data,
• scientific knowledge, and
• scientific communities
in everyday discoveries and in revolutionary shifts.
Importance of New Kinds of Data
Scientific discoveries often grow out of new methods for data
collection and new types of data. Consider
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Lavoisier’s emphasis on weight and measurements;
Brahe’s regular observations of celestial objects;
Darwin’s observations of animals across the planet; and
Franklin’s x-ray diffraction images of DNA structure.
These advances required a combination of technical skill and an
appreciation of empirical rigor.
Notably Lavoisier and Darwin profited from their data, whereas
Brahe and Franklin’s observations led others to discoveries.
Chemistry: Antoine Lavoisier
Lavoisier revolutionized the methods and theory of chemistry.
While his contemporaries primarily observed and described the
changes in chemical substances, Lavoisier valued measurement.
Weighing objects within a bell jar before and after combustion
revealed the conservation of mass contrary to appearance.
This finding ultimately led to the
discovery of oxygen and the rejection
of the phlogiston theory.
Astronomy: Tycho Brahe
Brahe’s legacy are his systematic astronomical measurements
that were more accurate than any others available at the time.
His contribution reflected meticulousness and ingenuity in
• inventing and improving scientific instruments;
• inspecting and calibrating his instruments routinely; and
• stressing systematic and regular measurements of
astronomical objects.
Although Brahe worked on his own geocentric model
of the solar system, Johannes Kepler’s analysis of the
data ultimately produced an accurate heliocentric
model of planetary orbits.
Role of Theories and Models in Science
Theories and models hold a special place in scientific activity:
• they define the scope and focus of scientific investigation;
• they support predictions about experimental outcomes and
future observations; and
• they establish world views subject to challenge.
The history of science illustrates these roles. For example,
• Darwin’s theory of evolution suggested the search for a
mechanism of transmission;
• the periodic table lets chemists predict elemental properties;
• Newtonian physics led to the discovery of Neptune and Ceres;
• aesthetic values led to the rejection of Ptolemaic theory.
Periodic Table of Elements
Used to illustrate and predict elements and their properties.
The Discovery of Neptune
After predicting the orbit of Uranus using Newtonian theory,
Alexis Bouvard noticed irregularities in its observed orbit.
Bouvard conjectured that an unknown planet was causing the
discrepancy, but did not investigate.
John Adams and Urbain Le Verrier became independently aware
of Bouvard’s findings and eventually competed for the discovery.
Both Le Verrier and Adams applied Newtonian
theory and Bode’s law to predict the location
of the new planet. Ultimately Le Verrier’s
predictions led to the discovery of Neptune.*
* with considerable controversy
Ptolemy and Copernicus
Ptolemy’s geocentric theory of the universe dominated Western
science (and religion) for centuries.
This theory has planets moving in nested circular
motions that are uniform around an equant.
Copernicus considered the equant abhorrent as it
violated the tenet that planets travel at uniform
speeds around circular trajectories.
He developed a new, heliocentric theory
that, although no more accurate and no less
complex, removed the equant.
Scientific Communities
In principle, communities of scientists serve several purposes.
For instance, they
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transmit ideas across physical and disciplinary boundaries,
collaborate on research topics too large for any one lab,
motivate members through the competition for discovery, and
evaluate the merit of ideas and protect against fraud.
A scientific community has elements of enablement and
suppression. History has shown scientists as progressively
entertaining new ideas, but conservative in their acceptance.
Watson, Crick, and Everyone Else
Watson and Crick are almost synonymous with the discovery of
DNA, but other groups worked simultaneously:
• Linus Pauling’s laboratory at Caltech and
• Maurice Wilkins and Rosalind Franklin at King’s College.
The atmosphere was competitive, but the discovery of DNA’s
structure was the combined work of several individuals, including
• William Bragg, Watson and Crick’s supervisor;
• Alfred Hershey and Martha Chase, who identified DNA (in
opposition to proteins) as the genetic material;
• Edward Ronwin, whose 1951 paper rekindled Pauling’s
interests in DNA structure; and many others.
In this case, the community was largely supportive of what was
ultimately a work of scientific progress.
Wegener and Continental Drift
Alfred Wegener proposed his theory of continental drift in 1912
when the dominant theory held that land mass was shaped by
the cooling of the earth.
Wegener’s observational evidence was strong, but his proposed
mechanism was untenable; the very idea required scientists to
abandon decades of theory.
Empirical discoveries in the 1950s led to
plate tectonics as a mechanism that
supported many of Wegener’s claims.
Although Wegener’s theory was initially
entertained as reasonable, eventually the
scientific community became openly hostile,
suppressing progress for decades.
Scientific Revolutions
One can view the history of science as successive revolutions that
dramatically alter scientific concepts and mechanisms:
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Wegener’s theory of continental drift transformed geology;
Copernicus’ heliocentric theory transformed astronomy;
Lavoisier’s oxygen theory transformed chemistry;
Newton’s theory of physics displaced the Cartesian model;
Einstein’s theories revolutionized Newtonian physics;
Skinner’s behaviorist movement transformed psychology;
Chomsky, Miller, Newell, Simon, and others overthrew
behaviorism for a renewed cognitive psychology.
These revolutions occur within the context of history and are
driven by methodological, personal, and social forces.
History and Philosophy of Science
The history and philosophy of science plays a dual role for
informatics research.
Philosophy of Science provides theories about how science
should or does function that informatics researchers can appeal
to as general principles for interactive systems.
History of Science provides data with which those researchers
can evaluate theories of science and abduce new explanations
for observed courses of behavior.
Together this rich context can lead us toward general informatics
systems that benefit a broad range of scientific researchers.