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		successful learning is open to question, because linguistic development does not always culminate in the perfectly accurate, perfectly stable grammar envisioned in the definition of identification.

		The defects in the identification paradigm can be remedied only in light of detailed information about children's linguistic development. For the most part, the needed information seems not to be currently available. Consequently, we shall not in this book defend the empirical adequacy of any specific model of language acquisition. Rather, the chapters that follow survey a variety of paradigms of varying relevance to intellectual development and to scientific inquiry. The survey, it may be hoped, will suggest questions about linguistic development whose answers can be converted into useful constraints on theories of comparative grammar. It may also suggest new ways of thinking about scientific discovery, both from the normative point of view, and from the point of view of machine implementation.

		The present section provides a glimpse of the vast array of paradigms that can be defined (more comprehensive treatment begins in Chapter 5). We shall modify the identification paradigm by narrowing, in turn, its interpretations of "scientist" and "data."

		§3.8 Memory-Limited Scientists

		It seems evident that children have limited memory for the sentences presented to them. Once processed, sentences are likely to be quickly erased from the child's memory. Here we shall consider scientists that undergo similar information loss. The following notation is used.

		3.31 Definition Let be given.

		(a) The result of removing the last member of  s  is denoted by  s -; if , then .

		(b)  — i.e., the last member of  s  — is denoted by  s last; if , then  s last = #.

		The following definition says that a scientist is memory-limited if her current conjecture depends on no more than her last conjecture and the current datum.

		3.32 Definition (Wexler and Culicover [194]) Scientist F is memory limited just in case for all , if and , then .