Susan A. Gelman
This paper addresses concept development in preschool children, based on recent psychological research. Over the past 30 years, there have been more than 7,000 journal articles written on children’s concepts or categories. Scholars are attracted by the opportunity to understand fundamental theoretical issues (How can we characterize early thought? How does it change over time?) as well as by the practical concern of determining how children reason about concepts that are directly relevant to their lives and schooling (including mathematics, biology, and physics).
Four key themes have emerged from recent research. They will be highlighted and illustrated in this paper.
These four themes contradict some widely held (but erroneous) views of early concepts, and they raise a variety of issues regarding early education.
Concepts provide an efficient way of organizing experience. If children were unable to categorize, their experiences would be chaotic—filled with objects, properties, sensations, and events too numerous to hold in memory. In contrast to this hypothesized “blooming, buzzing confusion” (to use the words of William James), children from earliest infancy form categories that are remarkably similar to those of adults. Before they have even begun to speak, infants form categories of faces, speech sounds, emotional expressions, colors, objects, animals, and mappings across modalities (see Gelman 1996 for review). By 18 months of age, most children have begun a vocabulary “explosion,” adding roughly nine new words each day to their vocabulary (Carey 1978). Assuming that most new words encode concepts, this fact suggests that one- and two-year-old children are adept at concept acquisition.
However, concepts do more than organize information efficiently in memory. They also serve an important function for a range of cognitive tasks, including identifying objects in the world, forming analogies, making inferences that extend knowledge beyond what is already known, and conveying core elements of a theory. Many of these tasks are central to school performance; thus, concepts can be thought of as the building blocks to these more complex skills.
One of these cognitive functions, known as induction, is the focus of the following discussion. Induction involves how concepts foster inferences about the unknown.
Both children and adults use categories to extend knowledge beyond what is obvious or already known (Carey 1985; Gelman and Markman 1986, 1987). For example, if four-year-old children are told a new fact, such as that a particular dog has leukocytes inside it, they are likely to infer that other dogs also have leukocytes inside them. It is important to note that children form such inferences even when they are not supported by outward appearances. In one Gelman and Markman example items children saw a brontosaurus, a rhinoceros, and a triceratops, which were labeled as “dinosaur,” “rhinoceros,” and “dinosaur,” respectively. Category labels and outward appearances conflicted: The brontosaurus and triceratops are members of the same category, whereas the rhinoceros and triceratops look more alike outwardly. Then children learned a new property of the brontosaurus and the rhinoceros—that they had cold blood and warm blood, respectively. They were asked which property was true of the triceratops. When children were informed that both the brontosaurus and the triceratops were dinosaurs, they inferred that the triceratops has cold blood like the brontosaurus, even though it more closely resembled the rhinoceros. The results of this and other related experiments showed that by 2-1/2 years of age, children base inferences on category membership, despite conflicting surface appearances (Gelman and Coley 1990).
Although induction can be viewed as positive because it allows children to expand their knowledge base, it also poses some problems for young children when they draw inappropriately broad inferences. One problem that results is stereotyping. Preschoolers often treat social categories as if they were biological categories, assuming, for example, that members of a social category (a category that is based on gender or race) will be alike with respect to ability or occupation (Hirschfeld 1996; Taylor 1996). A second problem is that young children at times ignore relevant information about statistical variation within a category (Lopez et al. 1992; Gutheil and Gelman 1997). For example, four-year-olds do not seem to realize that a property known to be true of five birds provides a firmer basis of induction than a property known to be true of only one bird. They also do not seem to realize that variability in a category is relevant to the kinds of inductions that are plausible.
In sum, this theme illustrates four important points:
On many traditional accounts, conceptions are said to undergo a fundamental, qualitative shift with development. That is, children and adults are often said to occupy opposite endpoints of various dichotomies, moving from perceptual to conceptual (Bruner et al. 1966), from concrete to abstract (Piaget 1951), or from similarity to theories (Quine 1977).
These developmental dichotomies are intuitively appealing, in part because children often do seem to reason in ways that are strikingly different from how adults reason. For example, in the well-known “conservation error” studied by Piaget, children under six or seven years of age report that an irrelevant transformation leads to a change in quantity (e.g., concluding that the amount of a liquid increases when it is simply poured from a wide container into a taller, narrower container). Children appear to focus on one salient but misleading dimension—for example, the height of a container—forgoing a deeper conceptual analysis. Throughout the past several decades, there have been many demonstrations that young children are “prone to accept things as they seem to be, in terms of their outer, perceptual, phenomenal, on-the-surface characteristics” (Flavell 1977).
However, as an account of what children are capable of doing, such developmental dichotomies as the “perceptual-to-conceptual shift” are inadequate (also Bauer and Mandler 1989; Gelman 1978; Gibson and Spelke 1983; Markman and Hutchinson,1984; Nelson 1977). With appropriately sensitive tasks, children can display abilities that do not appear in their everyday actions. (See Theme 3, Expertise and Task Effects Across Areas. See also Gelman and Baillargeon 1983 for extensive discussion.)
Indeed, not only are children capable of overcoming misleading appearances, they are even able to reason about concepts that are altogether non-obvious. Several scholars have recently begun studying how three- to five-year-old children reason about non-obvious entities across a range of topic areas, including:
Although for most of these topics preschool children have very little in the way of detailed, concrete knowledge, they have begun to appreciate that these non-obvious constructs exist and how they affect other, more observable outcomes and behaviors. For example, even three-year-olds have a core understanding that “germs” can cause illness and that foods may appear clean, yet still have disease-causing germs (Kalish 1996). It is intriguing that children are capable of this understanding at an age when they have not yet learned anything about the mechanisms by which viruses and bacteria affect human physiology (Au and Romo 1998). That children are open to reasoning about these topics and that they do so with considerable accuracy, despite an impoverished knowledge base, argues strongly that non-obvious entities are not beyond the capacity of preschool children.
The previous section illustrated that detailed knowledge is not a prerequisite for learning some of the core concepts in a domain (such as “germs”). Nonetheless, specialized knowledge can exert surprisingly powerful effects on cognition (Hirschfeld and Gelman 1994; Wellman and Gelman 1997). Twenty-five years ago, Chase and Simon (1973) found that chess experts have superior memory for the position of pieces on a chessboard, although they are no better than non-experts in their memory for digits. Chi (1978) demonstrated the same phenomenon in children: Child chess experts even outperform adult chess novices, which is an interesting reversal of the more usual developmental finding. In these examples, experts are not in general more intelligent or more skilled than novices. The effects are localized within the domain of expertise.
Regarding concept development, too, the child’s level of sophistication varies markedly by content area (Keil 1989, in press). Chi, Feltovich, and Glaser (1981), focusing on the domain of physics, found that expert problem-solvers and novice problem-solvers approach word problems about physics quite differently. They focus on altogether different features of the task. Similarly, Chi, Hutchinson, and Robin (1989) found that dinosaur experts who are children perform differently from novices in how they reason about the domain of dinosaurs; they generate a richer set of inferences and causal explanations.
Conceptual structure varies not only by domain but also by task. Even within a domain, children use different information in different contexts, depending on the task or function at hand (Deak and Bauer 1995, 1996; Taylor and Gelman 1993). For example, children display markedly different strategies for sorting pictures into groups, depending on whether the researcher provides the standard open-ended instructions (“See this picture? Can you find another one?”) or whether the researcher teaches the child a new word and asks the child to extend it (“See this dax? Can you find another dax?”) (Markman 1989). Similarly, children provide altogether different responses when they are asked to come up with the category label for an ambiguous item versus when they are asked to come up with a property inference for an ambiguous item that has been labeled by the experimenter (Gelman et al. 1986). Children consider a variety of information and flexibly deploy different sorting strategies depending on the task; they display links between task and strategy that are precise and predictable. These variations in performance are not random or idiosyncratic. Rather, they reveal that concepts have multiple functions, even for preschool children, and that children have learned to attend to different kinds of information, depending on the task at hand.
Adults’ concepts are influenced by theoretical belief systems. This statement can be readily illustrated with a very simple example. Until recently, a biological mother could be defined or understood as the woman who gives birth to a child. More recently, however, with new reproductive technology (including surrogate mothers and donor eggs), a biological mother need not be the woman who gives birth. Thus, even a concept so basic and fundamental as “mother” undergoes change as one’s theory of reproduction changes (which itself is influenced by changing technology).
A central developmental question is when and how children begin to incorporate theories into their concepts. One long-held view was that children’s initial categories are similarity-based and that children only begin to incorporate theories as they gain experience and formal schooling (Quine 1977). Likewise, Piaget argued that pre-operational children do not have the logical capacity to construct either theories or true concepts.
In contrast, many researchers now believe that concept acquisition in childhood may require theories. Murphy (1993) notes that theories help concept learners in three respects:
• Theories help identify those features that are relevant to a concept.
• Theories constrain how (e.g., along which dimensions) similarity should be computed.
• Theories can influence how concepts are stored in memory.
The implication here is that concept acquisition may proceed more smoothly with the help of theories. If true, it is reasonable to expect that theories may play a role in children’s concepts, even though the theories themselves are changing developmentally.
Indeed, recent studies provide compelling demonstrations that young children use theoretical knowledge to decide how to categorize data. Barrett, Abdi, Murphy, and Gallagher (1993) presented data suggesting that children’s intuitive theories help determine which properties and which feature correlations children select in making classifications. For example, in a task that required children to categorize novel birds into one of two novel categories, first- and fourth-grade children noticed the association between brain size and memory capacity and used that correlation to categorize new members. Specifically, exemplars that preserved the correlation were more often judged to be category members and to be more typical of the category. The children did not make use of features that correlated equally well—features that were presented together equally often in the input—but that were not supported by a theory—for example, the correlation between the structure of a heart and the shape of a beak.
In a second experiment, Barrett et al. (1993) found that children selected different feature-pairs, depending again on whether they were supported by a pre-existing theory. Third-grade children were presented with hypothetical categories that were described as either animals or tools. They then learned five properties about each category. When the category was described as an animal, children selectively focused on correlations between one subset of the properties, for example, “is found in the mountains” and “has thick wool.” In contrast, when the category was described as a tool, children selectively focused on correlations between a different subset of properties, for example, “is found in the mountains” and “can crush rocks.” These studies show that children focus their attention strategically on information that is relevant to the implicit theory they have formed.
More generally, errors in children’s theories may constrain or shape children’s concepts. One brief example illustrates children’s number concepts. Rochel Gelman has found that for preschool children and early elementary school children their understanding of arithmetic is heavily influenced by the theory that numbers are countable entities, starting with one and continuing sequentially by adding whole numbers. Based on this assumption, children experience tremendous difficulty when first encountering fractions, often treating them as if they were whole numbers (Gelman and Williams 1997). For example, when asked to sort cards (representing different amounts) onto a number line, children will treat a card with 1-1/2 circles on it as if it represented “2” on the number line. The difficulty children have here is not simply that they are encountering a new set of mathematical operations but that their prior theory clashes with the new system they have encountered. Similarly, theory-driven errors can be found in young children’s reasoning about physics (Kaiser et al. 1986) and biology (Carey 1985; Coley 1993).
Although a number of studies have begun to examine the influence of theories on early concepts, little work addresses the reverse question, that is, the influence of concepts on early theories. However, it seems plausible that certain conceptual assumptions may constrain aspects of children’s theories. For example, children appear to hold an “essentialist” assumption about categories (Gelman et al. 1994; Medin and Ortony 1989; Atran 1993), treating members of a category as if they have an underlying “essence” that can never be altered or removed. Essentialism is more compatible with creationist views than with evolutionary views of species origins (Mayr 1988), and it may even discourage children’s learning of evolutionary theory (Evans 1994). Thus, the structure of early concepts may have broader implications for science education.
The brief summary in this paper shatters several myths about children’s early concepts, including
To the contrary, recent evidence documents that even preschool children make use of concepts to expand knowledge via inductive inferences, that children’s concepts are heterogeneous and do not undergo qualitative shifts during development, and that children’s concepts incorporate non-perceptual elements from a young age.
Given that children’s concepts are in fact far more sophisticated than has been traditionally assumed, it becomes all the more important to ensure that early education exploits the capabilities that young children have. At the same time, given the close link between early concepts and emerging theories, one of the central challenges is to help children overcome pervasive faulty theories, some of which appear to persist into adulthood.
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Susan A. Gelman is a professor of psychology at the University of Michigan-Ann Arbor.
Copyright © 1999 by the American Association for the Advancement of Science (AAAS)