Pat LangleyPat Langley

Institute for the Study of Learning and ExpertiseInstitute for the Study of Learning and Expertiseandand

Center for the Study of Language and InformationCenter for the Study of Language and InformationStanford University, Stanford, CaliforniaStanford University, Stanford, California

http://www.isle.org/~langleyhttp://www.isle.org/~langley

langley@csli.stanford.edulangley@csli.stanford.edu

Heuristics for DiscoveryHeuristics for Discoveryin Cognitive Sciencein Cognitive Science

Herbert A. Simon’s LegacyHerbert A. Simon’s Legacy

Heuristics and Scientific DiscoveryHeuristics and Scientific Discovery

the heuristic nature of human problem solvingthe heuristic nature of human problem solving

the processes of scientific reasoning and discoverythe processes of scientific reasoning and discovery

Herbert Simon was fascinated by many phenomena, but two that Herbert Simon was fascinated by many phenomena, but two that drew his attention repeatedly were: drew his attention repeatedly were:

Thus, it seems appropriate to review Simon’s career in terms of Thus, it seems appropriate to review Simon’s career in terms of his personal heuristics for scientific research.his personal heuristics for scientific research.

Moreover, it makes sense to illustrate these rules of thumb with Moreover, it makes sense to illustrate these rules of thumb with examples from his own work on the discovery process. examples from his own work on the discovery process.

Be AudaciousBe Audacious

Understand the cognitive and computational mechanisms that Understand the cognitive and computational mechanisms that support the processes of scientific discovery.support the processes of scientific discovery.

Tackle challenging problems that others have been reluctant to Tackle challenging problems that others have been reluctant to face or even admit are solvable.face or even admit are solvable.

In 1966, Herb Simon published “Scientific Discovery and the In 1966, Herb Simon published “Scientific Discovery and the Psychology of Problem Solving”.Psychology of Problem Solving”.

This radical paper set the agenda for research on computational This radical paper set the agenda for research on computational scientific discovery for the next 35 years. scientific discovery for the next 35 years.

Ignore Discipline BoundariesIgnore Discipline Boundaries

To understand scientific discovery, borrow concepts not only To understand scientific discovery, borrow concepts not only from cognitive psychology and AI, but also from the history from cognitive psychology and AI, but also from the history and philosophy of science.and philosophy of science.

Become familiar with every field relevant to your research problem Become familiar with every field relevant to your research problem and incorporate the best ideas from each one. and incorporate the best ideas from each one.

Herb Simon applied his Renaissance scholarship to his discovery Herb Simon applied his Renaissance scholarship to his discovery research, as he did to many other scientific problems. research, as he did to many other scientific problems.

Moreover, he made his results accessible to members of all these Moreover, he made his results accessible to members of all these communities by publishing in many literatures.communities by publishing in many literatures.

Use a Secret WeaponUse a Secret Weapon

Cast the discovery task in terms of heuristic search through a Cast the discovery task in terms of heuristic search through a problem space controlled by a production system. problem space controlled by a production system.

Take advantage of metaphors and tools that you have mastered Take advantage of metaphors and tools that you have mastered but that are not yet widely available.but that are not yet widely available.

Herb Simon repeatedly invoked the notion of heuristic search to Herb Simon repeatedly invoked the notion of heuristic search to model the discovery process, as to many other phenomena.model the discovery process, as to many other phenomena.

However, he was also ready to share his secret weapons with any However, he was also ready to share his secret weapons with any who were willing to learn them. who were willing to learn them.

Balance Theory and DataBalance Theory and Data

Examine discoveries from the history of science that require Examine discoveries from the history of science that require computational explanation.computational explanation.

Constrain these historical models using established knowledge Constrain these historical models using established knowledge about human cognition. about human cognition.

Realize that scientific models must explain observations but also Realize that scientific models must explain observations but also remain connected to existing knowledge.remain connected to existing knowledge.

Herb Simon’s work on scientific discovery maintained a balance Herb Simon’s work on scientific discovery maintained a balance between theory and data, as did his other research efforts. between theory and data, as did his other research efforts.

SatisficeSatisfice

Focus on the discovery of descriptive laws from numeric data, Focus on the discovery of descriptive laws from numeric data, producing Bproducing BACONACON and its successors. and its successors.

Focus on discovery of simple structural models from qualitative Focus on discovery of simple structural models from qualitative data, producing Sdata, producing STAHLTAHL and D and DALTONALTON..

Ignore issues of problem formulation, variable selection, and Ignore issues of problem formulation, variable selection, and other aspects of scientific reasoning. other aspects of scientific reasoning.

Address challenging problems but idealize them enough to make Address challenging problems but idealize them enough to make them tractable.them tractable.

However, Herb Simon always acknowledged the limits of a However, Herb Simon always acknowledged the limits of a given idealization and the need for additional research.given idealization and the need for additional research.

PerseverePersevere

Herb Simon and his colleagues worked steadily, for over two Herb Simon and his colleagues worked steadily, for over two decades, to model the process of scientific discovery.decades, to model the process of scientific discovery.

Moreover, his research with Deepak Kulkarni on KMoreover, his research with Deepak Kulkarni on KEKADAEKADA itself modeled this central aspect of science. itself modeled this central aspect of science.

Science is a gradual process. Build incrementally on your previous Science is a gradual process. Build incrementally on your previous results, extending them to cover ever more phenomena.results, extending them to cover ever more phenomena.

The resulting body of research helped change the face of cognitive The resulting body of research helped change the face of cognitive science and clarified the computational nature of discovery. science and clarified the computational nature of discovery.

Evolution of Research on Evolution of Research on Computational Scientific DiscoveryComputational Scientific Discovery

1989 19901979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Bacon.1–Bacon.5Abacus,Coper

Fahrenheit, E*,Tetrad, IDSN

Hume,ARC

DST, GPN

LaGrangeSDS

SSF, RF5,LaGramge

Dalton,Stahl

RL, Progol

Gell-MannBR-3,

MendelPauli

Stahlp,Revolver

Dendral

AM Glauber NGlauberIDSQ,

Live

IECoast, Phineas,AbE, Kekada

Mechem, CDPAstra,GPM

HR

BR-4

Numeric laws Qualitative laws Structural models Process modelsLegendLegend

Applications of Computational DiscoveryApplications of Computational Discovery

Over the past decade, systems of this type have helped discover Over the past decade, systems of this type have helped discover new knowledge in many scientific fields: new knowledge in many scientific fields:

• stellar taxonomies from infrared spectra (Cheeseman et al., 1989)stellar taxonomies from infrared spectra (Cheeseman et al., 1989)

• qualitative chemical factors in mutagenesis (King et al., 1996)qualitative chemical factors in mutagenesis (King et al., 1996)

• quantitative laws of metallic behavior (Sleeman et al., 1997)quantitative laws of metallic behavior (Sleeman et al., 1997)

• qualitative conjectures in number theory (Colton et al., 2000)qualitative conjectures in number theory (Colton et al., 2000)

• temporal laws of ecological behavior (Todorovski et al., 2000)temporal laws of ecological behavior (Todorovski et al., 2000)

• reaction pathways in catalytic chemistry (Valdes-Perez, 1994, 1997)reaction pathways in catalytic chemistry (Valdes-Perez, 1994, 1997)

Each of these has led to publications in the refereed literature Each of these has led to publications in the refereed literature of the relevant scientific field. of the relevant scientific field.

Revising an Ecosystem ModelRevising an Ecosystem Model

GivenGiven: A model of Earth’s ecosystem (CASA) stated as difference : A model of Earth’s ecosystem (CASA) stated as difference equations that involve observable and hidden variables.equations that involve observable and hidden variables.

GivenGiven: Values of observable variables (rainfall, sunlight, NPP) as : Values of observable variables (rainfall, sunlight, NPP) as they change over both time and space.they change over both time and space.

FindFind: A revised ecosystem model with altered equations and/or : A revised ecosystem model with altered equations and/or parametric values that better fits the data.parametric values that better fits the data.

NPPc

IPAR

PET

T1T2We_max

E

EET

Tempc

Topt

NDVI

SOLAR

AHI

A

PETTWM

SR

FPAR

VEG

Revising Process Models of PhotosynthesisRevising Process Models of Photosynthesis

GivenGiven: Observed expression levels, over time, of the organism’s : Observed expression levels, over time, of the organism’s genes under conditions of high light.genes under conditions of high light.

FindFind: A revised model with altered reactions and regulations that : A revised model with altered reactions and regulations that explains the expression levels and the bleaching process.explains the expression levels and the bleaching process.

GivenGiven: Qualitative knowledge about reactions and regulations for : Qualitative knowledge about reactions and regulations for Cyanobacteria in a high ultraviolet situation. Cyanobacteria in a high ultraviolet situation.

LightLight

NBLSNBLS RRRRNBLRNBLR

NBLANBLA

GreenGreen

NBLBNBLB

CACBCACB

PSBA2PSBA2 PSABPSAB

PSBFPSBF

--

++

--

--

++

++++

++

++

--

--++

A Long-Term GoalA Long-Term Goal

The ultimate challenge in discovery research is to model the The ultimate challenge in discovery research is to model the behavior of a scientist who:behavior of a scientist who:

• Formulates the notion of satisficing in human decision makingFormulates the notion of satisficing in human decision making

• Co-invents list processing and heuristic search on computersCo-invents list processing and heuristic search on computers

• Co-develops theories of human memory and problem solving Co-develops theories of human memory and problem solving

• Uses his theories to model discovery and other key phenomenaUses his theories to model discovery and other key phenomena

• Fosters a new field that acknowledges no discipline boundariesFosters a new field that acknowledges no discipline boundaries

We know some of this scientist’s heuristics, and we have We know some of this scientist’s heuristics, and we have detailed records of his accomplishments, but the task remains detailed records of his accomplishments, but the task remains daunting. daunting.

A Closing QuotationA Closing Quotation

We would like to imagine that the great discoverers, the scientists We would like to imagine that the great discoverers, the scientists whose behavior we are trying to understand, would be pleased with whose behavior we are trying to understand, would be pleased with this interpretation of their activity as normal (albeit high-quality) this interpretation of their activity as normal (albeit high-quality) human thinking. . . human thinking. . .

But science is concerned with the way the world is, not with how But science is concerned with the way the world is, not with how we would like it to be. So we must continue to try new experiments, we would like it to be. So we must continue to try new experiments, to be guided by new evidence, in a heuristic search that is never to be guided by new evidence, in a heuristic search that is never finished but always fascinating. finished but always fascinating.

Herbert A. Simon, Envoi to Herbert A. Simon, Envoi to Scientific DiscoveryScientific Discovery, 1987. , 1987.