Falsifiability - 1 In science and philosophy of science, falsifiability, contingency, and...

Falsifiability - 1Falsifiability - 1

In science and philosophy of science, In science and philosophy of science,

falsifiabilityfalsifiability, , contingencycontingency, and , and defeasibilitydefeasibility

are roughly equivalent terms referring to are roughly equivalent terms referring to

the the propertyproperty of empirical of empirical statementsstatements that that

they must they must admitadmit of logical of logical counterexamplescounterexamples..

This stands in This stands in contradistinction tocontradistinction to formal formal

and mathematical statements that may be and mathematical statements that may be

tautologiestautologies, that is, universally true by dint , that is, universally true by dint

of definitions, axioms, and proofs.of definitions, axioms, and proofs.


Some philosophers and scientists, most Some philosophers and scientists, most

notably notably Karl PopperKarl Popper, have asserted that no , have asserted that no

empirical hypothesis, proposition, or theory empirical hypothesis, proposition, or theory

can be considered can be considered scientificscientific ifif it does not it does not

admit the admit the possibilitypossibility ofof a a contrarycontrary case. case.

For example, the proposition For example, the proposition "all swans are "all swans are

white"white" would be would be falsified byfalsified by observing a observing a

black swanblack swan, which would in turn depend on , which would in turn depend on

there being a black swan somewhere in there being a black swan somewhere in

existence.existence.


A A falsifiable propositionfalsifiable proposition or theory or theory mustmust definedefine

in some way in some way what iswhat is, or will be, , or will be, forbiddenforbidden by by

that proposition or theory.that proposition or theory.

For example, the existence of a black swan is For example, the existence of a black swan is

forbidden by the proposition in question. The forbidden by the proposition in question. The

possibility in principle of possibility in principle of observingobserving a a black black

swanswan as a as a counterexample tocounterexample to the general the general

propositionproposition is sufficient to qualify the is sufficient to qualify the

proposition as falsifiable.proposition as falsifiable.


The falsification of statements occurs The falsification of statements occurs through through modus tollensmodus tollens, via some , via some observation.observation.

Suppose some universal statement Suppose some universal statement UU implies an observation implies an observation OO ::

U U →→ OO An observation conflicting with An observation conflicting with O O , however, , however,

is made:is made: ¬ ¬ OO

So by So by modus tollens modus tollens ::

¬ ¬ UU


It is always It is always possiblepossible to to reviserevise the universal the universal statementstatement or the existential statement so or the existential statement so that that falsificationfalsification does does not occurnot occur..

On hearing that a black swan has been On hearing that a black swan has been observed in Australia, one might introduce observed in Australia, one might introduce the the ad hocad hoc hypothesis, hypothesis, ""all swans are all swans are white except those found in Australiawhite except those found in Australia""..

The universal statement isThe universal statement is defeasibledefeasible through through exceptionsexceptions. And there may be . And there may be exceptions to the exceptions.exceptions to the exceptions.


Naïve falsificationNaïve falsification considers scientific considers scientific statements individually. But scientific statements individually. But scientific theoriestheories are formed from are formed from groups ofgroups of these sorts of these sorts of statementsstatements, and it is these groups that must be , and it is these groups that must be accepted or rejected by scientists. Scientific accepted or rejected by scientists. Scientific theoriestheories can always be can always be defended bydefended by the the addition of addition of ad hocad hoc hypotheses hypotheses..

As Popper put it, a As Popper put it, a decisiondecision is required on the is required on the part of the scientist to part of the scientist to acceptaccept or or rejectreject the the statementsstatements that go to make up a theory or that that go to make up a theory or that might falsify it.might falsify it.

Falsifiability - 7Falsifiability - 7 At some point, the At some point, the weightweight ofof the the ad hocad hoc

hypotheseshypotheses andand disregardeddisregarded falsifying falsifying observationsobservations will become so great that it will become so great that it becomesbecomes unreasonableunreasonable to support the base theory any longer, and a to support the base theory any longer, and a decision will be made to reject it.decision will be made to reject it.

In place of naïve falsification, Popper envisioned In place of naïve falsification, Popper envisioned sciencescience as as evolvingevolving by the successive by the successive rejectionrejection ofof falsified falsified theoriestheories, rather than falsified statements., rather than falsified statements.

Falsified Falsified theoriestheories are to be are to be replacedreplaced by theoriesby theories that account for the phenomena which falsified the that account for the phenomena which falsified the prior theory, i.e. with prior theory, i.e. with greatergreater explanatory powerexplanatory power. .

Falsifiability - 8Falsifiability - 8 PopperPopper proposed falsification as a way to proposed falsification as a way to

determine if a theory is scientific. If a determine if a theory is scientific. If a theorytheory is is falsifiablefalsifiable, then it is , then it is scientificscientific; if it is not, then it is ; if it is not, then it is not science. A theory not open to falsification not science. A theory not open to falsification requires requires faithfaith that it is not false. He uses this that it is not false. He uses this criterion of demarcationcriterion of demarcation to draw a sharp line to draw a sharp line between scientific and unscientific theories.between scientific and unscientific theories.

FalsifiabilityFalsifiability was one of the criteria was one of the criteria usedused by by JudgeJudge Overton to Overton to determinedetermine that that 'creation science''creation science' was was not scientificnot scientific and should not be taught in public and should not be taught in public schools. It was enshrined in United States law for schools. It was enshrined in United States law for whether whether scientificscientific evidenceevidence is is admissibleadmissible inin a jury a jury trialtrial. .

Belief Revision- 1Belief Revision- 1

Belief revisionBelief revision is the is the processprocess of changing of changing beliefs to beliefs to take into accounttake into account a a newnew piece of piece of informationinformation..

The logical The logical formalizationformalization of of belief revisionbelief revision is is researched in philosophy, in databases, and in researched in philosophy, in databases, and in artificial intelligenceartificial intelligence for the design of for the design of rationalrational agentsagents..

What makes What makes belief revision non-trivialbelief revision non-trivial is that is that several different ways for performing this several different ways for performing this operation may be possible.operation may be possible.


E.g., the current knowledge includes the 3 E.g., the current knowledge includes the 3 facts: “facts: “AA is true is true”, “”, “BB is true is true” and “” and “if if AA and and BB are true then are true then CC is true is true”.”.

The The introductionintroduction of the new information “ of the new information “CC is falseis false” can be ” can be donedone preserving preserving consistencyconsistency only by only by removingremoving at least one at least one of the 3 of the 3 factsfacts. In this case, there are at least . In this case, there are at least 3 different ways for performing revision.3 different ways for performing revision.

In generalIn general, there may be , there may be severalseveral different different waysways for for changing knowledgechanging knowledge..

Belief Revision- 3Belief Revision- 3 Two kindsTwo kinds ofof changechange are usually distinguished: are usually distinguished: UpdateUpdate.. New information is about the New information is about the presentpresent, ,

while the old beliefs refer to the while the old beliefs refer to the pastpast; update ; update is the operation of is the operation of changing the old beliefschanging the old beliefs to to take into account the change. take into account the change.

RevisionRevision.. Both the Both the old beliefsold beliefs and the and the new new informationinformation refer to the refer to the same situationsame situation; an ; an inconsistency between them is explained by inconsistency between them is explained by the possibility of old information being less the possibility of old information being less reliable than the new one; revision is the reliable than the new one; revision is the process of process of insertinginserting the the new informationnew information into into the set of old beliefs the set of old beliefs withoutwithout generating an generating an inconsistencyinconsistency. .


The The main assumptionmain assumption of belief revision is that of belief revision is that

of of minimal changeminimal change: the knowledge before and : the knowledge before and

after the change should be as similar as after the change should be as similar as

possible.possible.

In the In the case ofcase of updateupdate, this principle , this principle

formalizes the formalizes the assumption ofassumption of inertiainertia..

In the In the case of revisioncase of revision, this principle enforces , this principle enforces

as much as much informationinformation as possible as possible to beto be

preserved by the changepreserved by the change..

Scientific method - 1Scientific method - 1 Scientific methodScientific method is a body of is a body of techniquestechniques forfor

investigatinginvestigating phenomenaphenomena and and acquiringacquiring newnew knowledgeknowledge, as well as for , as well as for correctingcorrecting andand integrating previous knowledgeintegrating previous knowledge. It is . It is based based onon observable, empirical, measurable observable, empirical, measurable evidenceevidence, and subject to , and subject to laws of reasoninglaws of reasoning..

Although specialized procedures vary from Although specialized procedures vary from one field of inquiry to another, there are one field of inquiry to another, there are identifiable identifiable featuresfeatures that that distinguish distinguish scientific inquiryscientific inquiry from other methods of from other methods of developing knowledge.developing knowledge.

Scientific method - 2Scientific method - 2

Scientific researchers propose Scientific researchers propose specificspecific hypotheses as hypotheses as explanationsexplanations of natural of natural phenomena, and design phenomena, and design experimentalexperimental studies studies that test these that test these predictionspredictions for accuracy. for accuracy.

These These stepssteps are are repeatedrepeated in order in order to maketo make increasingly increasingly dependabledependable predictionspredictions of future of future results. results.

TheoriesTheories that encompass whole domains of that encompass whole domains of inquiry serve to inquiry serve to bindbind more specific more specific hypotheseshypotheses together together intointo logically logically coherentcoherent wholeswholes. .


This in turn aids in the This in turn aids in the formationformation of of newnew hypotheseshypotheses, as well as in placing groups of , as well as in placing groups of specific hypotheses specific hypotheses into into aa broader broader contextcontext of understanding.of understanding.

Among other facets shared by the various Among other facets shared by the various fields of inquiry is the conviction that the fields of inquiry is the conviction that the processprocess must be must be objectiveobjective so that the so that the scientist does scientist does notnot biasbias the the interpretationinterpretation of of the results the results or changeor change the the resultsresults outright. outright.


Another basic expectation is that of Another basic expectation is that of making complete making complete documentationdocumentation of data of data andand methodologymethodology available for careful available for careful scrutinyscrutiny by otherby other scientists and scientists and researchers, thereby allowing other researchers, thereby allowing other researchers the opportunity to researchers the opportunity to verifyverify results byresults by attempted attempted reproductionreproduction of them. of them.

This also allows This also allows statistical measuresstatistical measures of the of the reliabilityreliability ofof the the resultsresults to be established. to be established.


There are multiple ways of outlining the There are multiple ways of outlining the basicbasic

methodmethod sharedshared by by allall of the of the fieldsfields of of scientificscientific

inquiryinquiry..

The The followingfollowing facetsfacets are are typicaltypical classifications classifications

of the most important of the most important componentscomponents ofof the the

methodmethod on which there is very on which there is very wide wide

agreementagreement in in the the scientificscientific communitycommunity and and

among philosophers of science.among philosophers of science.


ObservationObservation. A constant feature of scientific . A constant feature of scientific inquiry. inquiry.

DescriptionDescription. Information must be . Information must be reliablereliable, , i.e. replicable (i.e. replicable (repeatablerepeatable) as well as valid ) as well as valid ((relevantrelevant to the inquiry). to the inquiry).

PredictionPrediction. Information must be . Information must be validvalid forfor observations observations past, present, and futurepast, present, and future of of given phenomena, i.e. purported "one shot" given phenomena, i.e. purported "one shot" phenomena do not give rise to the phenomena do not give rise to the capability to predict, nor to the ability to capability to predict, nor to the ability to repeat an experiment. repeat an experiment.


ControlControl. . ActiveActively and ly and fairfairly ly samplingsampling the range the range of of possiblepossible occurrences occurrences, whenever possible and , whenever possible and proper, as opposed to the passive acceptance proper, as opposed to the passive acceptance of opportunistic data, is the best way to control of opportunistic data, is the best way to control or counterbalance the risk of empirical bias. or counterbalance the risk of empirical bias.

FalsifiabilityFalsifiability, or the , or the elimination ofelimination of plausible plausible alternativesalternatives. This is a . This is a gradual processgradual process that that requires requires repeated experimentsrepeated experiments by by multiplemultiple researchersresearchers who must be able to who must be able to replicatereplicate resultsresults in order to corroborate them. in order to corroborate them.


All hypotheses and theories are in principle All hypotheses and theories are in principle

subject to disproofsubject to disproof. There might be a . There might be a

consensus about a particular hypothesis or consensus about a particular hypothesis or

theory, yet it must in principle remain theory, yet it must in principle remain

tentative. tentative.

As a body of knowledge grows and a As a body of knowledge grows and a

particular hypothesis or particular hypothesis or theory repeatedlytheory repeatedly

brings brings predictablepredictable resultsresults, , confidenceconfidence in the in the

hypothesis or theory hypothesis or theory increasesincreases..


Causal explanationCausal explanation. The following . The following requirements are generally regarded as requirements are generally regarded as important to scientific understanding: important to scientific understanding:

– Identification of causesIdentification of causes. Identification of the . Identification of the causes of a particular phenomenon to the causes of a particular phenomenon to the best achievable extent. best achievable extent.

– Covariation of eventsCovariation of events. The hypothesized . The hypothesized causes must correlate with observed effects. causes must correlate with observed effects.

– Time-order relationshipTime-order relationship. The hypothesized . The hypothesized causes must precede the observed effects.causes must precede the observed effects.

Scientific method - 10Scientific method - 10 TestabilityTestability, a property applying to an empirical , a property applying to an empirical

hypothesis, involves two components:hypothesis, involves two components: The logical property described as contingency, The logical property described as contingency,

defeasibilitydefeasibility, or falsifiability, meaning that , or falsifiability, meaning that counterexamplescounterexamples to the hypothesis are to the hypothesis are notnot logically logically impossibleimpossible..

The practical The practical feasibilityfeasibility of of observing a observing a reproduciblereproducible series of such counterexamples, if series of such counterexamples, if they do exist.they do exist.

In short, a In short, a hypothesishypothesis is is testabletestable if there is some if there is some real hope of real hope of decidingdeciding whether it is whether it is true or falsetrue or false of of realreal experienceexperience. .

Scientific method - 11Scientific method - 11 The The predictive powerpredictive power of a scientific theory of a scientific theory

refers to its ability to generate refers to its ability to generate testabletestable predictionspredictions. .

TheoriesTheories with with strongstrong predictive powerpredictive power are are highly valuedhighly valued, because the predictions can , because the predictions can often encourage the falsification of the theory.often encourage the falsification of the theory.

The concept of predictive power differs from The concept of predictive power differs from explanatory or explanatory or descriptive powerdescriptive power (where (where phenomenaphenomena that are already known are that are already known are retrospectively explainedretrospectively explained by a given theory) in by a given theory) in that it allows a prospective that it allows a prospective test oftest of theoretical theoretical understandingunderstanding..


Scientific ideas that do not confer any Scientific ideas that do not confer any predictive power are considered at best predictive power are considered at best ""conjecturesconjectures", or at worst "", or at worst "pseudosciencepseudoscience". ". Because they cannot be tested or falsified in Because they cannot be tested or falsified in any way, there is no way to determine any way, there is no way to determine whether they are true or false, and so they do whether they are true or false, and so they do not gain the status of "not gain the status of "scientific theoryscientific theory".".

Theories whose "Theories whose "predictive powerpredictive power" " presupposes presupposes technologiestechnologies that are that are not not currently possiblecurrently possible constitute something of a constitute something of a grey areagrey area..


ReproducibilityReproducibility is one of the main principles is one of the main principles

of the of the scientific methodscientific method, and refers to the , and refers to the

ability of a ability of a testtest or experiment to be or experiment to be

accuratelyaccurately reproduced, or reproduced, or replicatedreplicated..

The term is very closely related to the The term is very closely related to the

concept of concept of testabilitytestability and, depending on and, depending on

the particular field, may require the test or the particular field, may require the test or

experimentexperiment to be to be falsifiablefalsifiable..

Scientific method - 14Scientific method - 14 The results of an The results of an experimentexperiment performed by a performed by a

group of researchers are generally group of researchers are generally evaluatedevaluated by other by other independentindependent researchersresearchers by by reproducingreproducing the original experiment. the original experiment.

They They repeatrepeat the same the same experimentexperiment themselves, themselves, based onbased on the original experimental the original experimental descriptiondescription, , and see if their experiment and see if their experiment givesgives similar resultssimilar results to those to those reportedreported by the original group. by the original group.

The result values are said to be The result values are said to be commensuratecommensurate if they are obtained (in distinct experimental if they are obtained (in distinct experimental trials) according to the trials) according to the samesame reproduciblereproducible experimentalexperimental descriptiondescription and and procedureprocedure..


ExperimentsExperiments which which cannotcannot be be reliablyreliably

reproducedreproduced are generally are generally notnot considered to considered to

provide useful provide useful scientific evidencescientific evidence..

ResultsResults which prove to be which prove to be highly highly

reproduciblereproducible are given are given more credencemore credence than than

those which are less reproducible, although those which are less reproducible, although

this is this is based onbased on an intuitive application of the an intuitive application of the

principle of inductionprinciple of induction, rather than on the , rather than on the

strict application of the principles of strict application of the principles of

falsifiability.falsifiability.

Science features – summary Science features – summary 11

ScienceScience is the organized, is the organized, systematicsystematic

enterprize that gathers enterprize that gathers knowledgeknowledge about the about the

worldworld and our theorizations and condenses it and our theorizations and condenses it

into into testable lawstestable laws and and principlesprinciples..

The The featuresfeatures of scienceof science that distinguish it that distinguish it

from pseudoscience are: from pseudoscience are: repeatabilityrepeatability, ,

economyeconomy, , mensurationmensuration, , heuristicsheuristics, ,

consilienceconsilience..


RepeatabilityRepeatability: The same phenomenon is : The same phenomenon is sought again, preferably by sought again, preferably by independentindependent investigation, and the interpretation given investigation, and the interpretation given to it is to it is confirmedconfirmed oror discardeddiscarded by means of by means of novel novel analysisanalysis and and experimentationexperimentation..

EconomyEconomy: Scientists attempt to : Scientists attempt to abstractabstract the the informationinformation into the into the formform that is both that is both simplestsimplest and aesthetically most and aesthetically most pleasingpleasing – – the combination called the combination called eleganceelegance – while – while yielding the yielding the largestlargest amount of amount of informationinformation with the with the leastleast amount of amount of efforteffort..


MensurationMensuration: If something come be properly : If something come be properly

measured, using measured, using universally accepted scalesuniversally accepted scales, ,

generalizations about it are rendered generalizations about it are rendered unambiguousunambiguous..

HeuristicsHeuristics: The best science : The best science stimulatesstimulates further further

discoverydiscovery, often in unpredictable , often in unpredictable new directionsnew directions; ;

and the new knowledge provides an and the new knowledge provides an additional testadditional test

of the original principles that led to its discovery.of the original principles that led to its discovery.

ConsilienceConsilience: The : The explanationsexplanations most likely to most likely to

survivesurvive, of different phenomena, are those that can , of different phenomena, are those that can

be be connectedconnected and proved and proved consistentconsistent with one with one

another.another.

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