Transcript Falsifiability - 1

Falsifiability - 1
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In science and philosophy of science, falsifiability,
contingency, and defeasibility are roughly
equivalent terms referring to the property of
empirical statements that they must admit of
logical counterexamples.
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This stands in contradistinction to formal and
mathematical statements that may be tautologies,
that is, universally true by dint of definitions,
axioms, and proofs.
Falsifiability - 2
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Some philosophers and scientists, most notably
Karl Popper, have asserted that no empirical
hypothesis, proposition, or theory can be
considered scientific if it does not admit the
possibility of a contrary case.
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For example, the proposition "all swans are
white" would be falsified by observing a black
swan, which would in turn depend on there
being a black swan somewhere in existence.
Falsifiability - 3
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A falsifiable proposition or theory must define in
some way what is, or will be, forbidden by that
proposition or theory.
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For example, the existence of a black swan is
forbidden by the proposition in question. The
possibility in principle of observing a black swan
as a counterexample to the general proposition is
sufficient to qualify the proposition as falsifiable.
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The falsification of statements occurs through
modus tollens, via some observation.
 Suppose some universal statement U implies an
observation O :
U →O
 An observation conflicting with O , however, is
made:
¬O
 So by modus tollens :
¬U
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It is always possible to revise the universal
statement or the existential statement so that
falsification does not occur.
 On hearing that a black swan has been observed
in Australia, one might introduce the ad hoc
hypothesis, "all swans are white except those
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found in Australia".
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The universal statement is defeasible through
exceptions. And there may be exceptions to the
exceptions.
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Naïve falsification considers scientific statements
individually. But scientific theories are formed
from groups of these sorts of statements, and it
is these groups that must be accepted or rejected
by scientists. Scientific theories can always be
defended by the addition of ad hoc hypotheses.
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As Popper put it, a decision is required on the
part of the scientist to accept or reject the
statements that go to make up a theory or that
might falsify it.
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At some point, the weight of the ad hoc hypotheses
and disregarded falsifying observations will become
so great that it becomes unreasonable to support
the base theory any longer, and a decision will be
made to reject it.
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In place of naïve falsification, Popper envisioned
science as evolving by the successive rejection of
falsified theories, rather than falsified statements.
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Falsified theories are to be replaced by theories that
account for the phenomena which falsified the prior
theory, i.e. with greater explanatory power.
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Popper proposed falsification as a way to determine
if a theory is scientific. If a theory is falsifiable, then
it is scientific; if it is not, then it is not science. A
theory not open to falsification requires faith that it
is not false. He uses this criterion of demarcation to
draw a sharp line between scientific and unscientific
theories.
 Falsifiability was one of the criteria used by Judge
Overton to determine that 'creation science' was not
scientific and should not be taught in public schools.
It was enshrined in United States law for whether
scientific evidence is admissible in a jury trial.
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Belief Revision- 1

Belief revision is the process of changing beliefs
to take into account a new piece of information.
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The logical formalization of belief revision is
researched in philosophy, in databases, and in
artificial intelligence for the design of rational
agents.
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What makes belief revision non-trivial is that
several different ways for performing this
operation may be possible.
Belief Revision- 2
E.g., the current knowledge includes the 3 facts:
“A is true”, “B is true” and “if A and B are true
then C is true”.
 The introduction of the new information “C is
false” can be done preserving consistency only
by removing at least one of the 3 facts. In this
case, there are at least 3 different ways for
performing revision.
 In general, there may be several different ways
for changing knowledge.
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Belief Revision- 3
Two kinds of change are usually distinguished:
 Update. New information is about the present,
while the old beliefs refer to the past; update is
the operation of changing the old beliefs to take
into account the change.
 Revision. Both the old beliefs and the new
information refer to the same situation; an
inconsistency between them is explained by the
possibility of old information being less reliable
than the new one; revision is the process of
inserting the new information into the set of old
beliefs without generating an inconsistency.
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Belief Revision- 4
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The main assumption of belief revision is that of
minimal change: the knowledge before and after
the change should be as similar as possible.
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In the case of update, this principle formalizes
the assumption of inertia.
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In the case of revision, this principle enforces as
much information as possible to be preserved by
the change.
Scientific method - 1
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Scientific method is a body of techniques for
investigating phenomena and acquiring new
knowledge, as well as for correcting and
integrating previous knowledge. It is based on
observable, empirical, measurable evidence,
and subject to laws of reasoning.
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Although specialized procedures vary from one
field of inquiry to another, there are identifiable
features that distinguish scientific inquiry from
other methods of developing knowledge.
Scientific method - 2
Scientific researchers propose specific hypotheses
as explanations of natural phenomena, and
design experimental studies that test these
predictions for accuracy.
 These steps are repeated in order to make
increasingly dependable predictions of future
results.
 Theories that encompass whole domains of
inquiry serve to bind more specific hypotheses
together into logically coherent wholes.
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Scientific method - 3
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This in turn aids in the formation of new
hypotheses, as well as in placing groups of
specific hypotheses into a broader context of
understanding.
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Among other facets shared by the various fields
of inquiry is the conviction that the process must
be objective so that the scientist does not bias
the interpretation of the results or change the
results outright.
Scientific method - 4
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Another basic expectation is that of making
complete documentation of data and
methodology available for careful scrutiny by
other scientists and researchers, thereby
allowing other researchers the opportunity to
verify results by attempted reproduction of
them.
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This also allows statistical measures of the
reliability of the results to be established.
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There are multiple ways of outlining the basic
method shared by all of the fields of scientific
inquiry.
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The following facets are typical classifications of
the most important components of the method
on which there is very wide agreement in the
scientific community and among philosophers of
science.
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Observation. A constant feature of scientific
inquiry.
 Description. Information must be reliable, i.e.
replicable (repeatable) as well as valid (relevant to
the inquiry).
 Prediction. Information must be valid for
observations past, present, and future of given
phenomena, i.e. purported "one shot" phenomena
do not give rise to the capability to predict, nor to
the ability to repeat an experiment.
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Scientific method - 7
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Control. Actively and fairly sampling the range of
possible occurrences, whenever possible and
proper, as opposed to the passive acceptance of
opportunistic data, is the best way to control or
counterbalance the risk of empirical bias.
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Falsifiability, or the elimination of plausible
alternatives. This is a gradual process that
requires repeated experiments by multiple
researchers who must be able to replicate results
in order to corroborate them.
Scientific method - 8
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All hypotheses and theories are in principle
subject to disproof. There might be a consensus
about a particular hypothesis or theory, yet it
must in principle remain tentative.
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As a body of knowledge grows and a particular
hypothesis or theory repeatedly brings
predictable results, confidence in the hypothesis
or theory increases.
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Causal explanation. The following requirements
are generally regarded as important to scientific
understanding:
– Identification of causes. Identification of the
causes of a particular phenomenon to the best
achievable extent.
– Covariation of events. The hypothesized causes
must correlate with observed effects.
– Time-order relationship. The hypothesized
causes must precede the observed effects.
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Testability, a property applying to an empirical
hypothesis, involves two components:
 The logical property described as contingency,
defeasibility, or falsifiability, meaning that
counterexamples to the hypothesis are not logically
impossible.
 The practical feasibility of observing a reproducible
series of such counterexamples, if they do exist.
 In short, a hypothesis is testable if there is some
real hope of deciding whether it is true or false of
real experience.
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The predictive power of a scientific theory refers
to its ability to generate testable predictions.
 Theories with strong predictive power are highly
valued, because the predictions can often
encourage the falsification of the theory.
 The concept of predictive power differs from
explanatory or descriptive power (where
phenomena that are already known are
retrospectively explained by a given theory) in
that it allows a prospective test of theoretical
understanding.
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Scientific ideas that do not confer any predictive
power are considered at best "conjectures", or
at worst "pseudoscience". Because they cannot
be tested or falsified in any way, there is no way
to determine whether they are true or false, and
so they do not gain the status of "scientific
theory".
 Theories whose "predictive power" presupposes
technologies that are not currently possible
constitute something of a grey area.
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Scientific method - 13
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Reproducibility is one of the main principles of
the scientific method, and refers to the ability
of a test or experiment to be accurately
reproduced, or replicated.
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The term is very closely related to the concept
of testability and, depending on the particular
field, may require the test or experiment to be
falsifiable.
Scientific method - 14
The results of an experiment performed by a
group of researchers are generally evaluated by
other independent researchers by reproducing
the original experiment.
 They repeat the same experiment themselves,
based on the original experimental description,
and see if their experiment gives similar results
to those reported by the original group.
 The result values are said to be commensurate if
they are obtained (in distinct experimental trials)
according to the same reproducible experimental
description and procedure.
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Scientific method - 15
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Experiments which cannot be reliably
reproduced are generally not considered to
provide useful scientific evidence.
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Results which prove to be highly reproducible
are given more credence than those which are
less reproducible, although this is based on an
intuitive application of the principle of induction,
rather than on the strict application of the
principles of falsifiability.
Science features – summary 1
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Science is the organized, systematic enterprize
that gathers knowledge about the world and our
theorizations and condenses it into testable laws
and principles.
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The features of science that distinguish it from
pseudoscience are: repeatability, economy,
mensuration, heuristics, consilience.
Science features – summary 2
Repeatability: The same phenomenon is sought
again, preferably by independent investigation,
and the interpretation given to it is confirmed or
discarded by means of novel analysis and
experimentation.
 Economy: Scientists attempt to abstract the
information into the form that is both simplest
and aesthetically most pleasing – the
combination called elegance – while yielding the
largest amount of information with the least
amount of effort.
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Science features – summary 3
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Mensuration: If something come be properly
measured, using universally accepted scales,
generalizations about it are rendered unambiguous.
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Heuristics: The best science stimulates further
discovery, often in unpredictable new directions;
and the new knowledge provides an additional test
of the original principles that led to its discovery.
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Consilience: The explanations most likely to survive,
of different phenomena, are those that can be
connected and proved consistent with one another.