Theory Formation by Heuristic Search

Ahwhine h'arning can be categorized along many dimcnsiotts, an important one o/ ~hich is "degree of human guidance or forethought'. Thi~ cotztintaon stretches from rote learning, through carefully-g,ided concept-fon~ation by obsert'ation, ot~t toward independent theory formation. Six)'ears ago. the ,~',t program was constructed as an experiment in this latter kind of leanffng by discot'ery, hs source of I~);~er ~as a large body of heuristics, rules which guhled it toward fruitful topics of int'estigation, toward profitable experiments to perform, toward platt~ible hypotheses and definitions. Since that time, we hate gained a deeper itt~ight into the nature of heuristics and the nature of the process of forming and extending theories empirically. "The Natttre of llettristics I" paper presented the theoretical basig for this work, with on emphasis on how heuristics relate to each other. This paper present.~ our accretion model of theory formation, and git'es many exatnple.~ of it.~ use in producing new discoveries in t'arious field~. These examples are drawn ]'rom runs of a program called Eur~ts~.o, the successor to AM. that embodies the accretion tnodel and uses a corptt~ of heuristics to guide its behat'ior. Since our tnodel demands the ability to discoter new heuristics periodically as well a~ new domain objects and operators, some of oar examples illustrate that process as well. "The Nature of ileuristics Ill" paper describes the architecture of the EURISKO program, and conchtsiot~ we hate made front its behar'ior. This paper deals with learning, by which we intend to include all processes which result in accretion of knowledge. Scction 1 surveys the spcctrum of learning, from rote memorization to more complex activities. Section 2 focuses on the far end of the learning spectrum, inductive inference. Section 3 proposes a model for the far end of that activity, empirical theory formation. That model accounts for the discovery of new heuristics as well as new task-specific objects and operations. Finally, Section 4 presents dozens of examples of the model in action, producing discovcrics in many different fields. The next paper in this