The chapters by Dedre Gentner, Keith Holyoak and Paul Thagard, and David Rumelhart in this volume present a broad spectrum of approaches to understanding the nature of analogical thought processes. Gentner spends a good deal of effort on formulating just what an analogy is; Holyoak and Thagard use production systems and spreading activation to simulate analogical processing in a problemsolving task; and Rumelhart explores the potential importance of connectionism for understanding analogies in the context of other “higher mental processes.” How are we to integrate this enormous diversity in tackling the same underlying problem? Is one right and the others wrong? Which proposals actually conflict, and which ones are compatible? What have we learned from each one about analogical thought?

I plan to approach these questions within a broad metatheoretical framework that spans the unique as well as the common aspects of the three presentations. The framework I have in mind is closely related to David Marr's (1982) well-known distinction among three levels of analysis of an information-processing (IP) system: the computational level, the algorithmic level, and the implementational level. My own view of the situation is slightly different from Marr's in that I see IP theories as spanning a single continuum of possible theoretical levels defined at the “upper” end of the spectrum by informational (or task) constraints, at the “lower” end by hardware constraints, and in between by behavioral constraints.