Much of our thinking occurs in the form of propositions, statements that express ideas. All propositions consist of concepts combined in a particular way. For example, “college students are intelligent people” is a proposition in which the two concepts “college students” and “intelligent people” are linked by the verb are.
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Concepts are basic units of semantic memory—mental categories into which we place objects, activities, abstractions (such as “liberal” and “conservative”), and events that have essential features in common. Every psychological term you are learning in this course is a concept. Concepts can be acquired through explicit instruction or through our own observations of similarities and differences among various objects and events.
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Many concepts are difficult to define explicitly. For example, you are quite familiar with the concept “vegetable,” yet you might have difficulty coming up with an explicit definition of what a vegetable is. However, you can quickly think of a good example of a vegetable, such as broccoli or carrots.
According to Eleanor Rosch, many concepts are defined by prototypes, the most typical and familiar members of a category, or class. Rosch suggests that we often decide which category something belongs to by its degree of resemblance to the prototype. Consider the following questions:
Is an eagle a bird?
Is a penguin a bird?
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Is a bat a bird?
According to the prototype view, you should have come to a quicker decision on the first question than on the last two. Why? Because an eagle fits most people’s “bird” prototype better than does a penguin (which is a bird, though it lacks some essential prototypic features, such as the ability to fly) or a bat (which is not a bird, even though it flies). Experiments measuring how quickly participants responded yes or no to the preceding questions have found that it does indeed take most people longer to decide whether penguins or bats are birds.
The use of prototypes is perhaps the most elementary method of forming concepts. It requires that we note only similarities among objects. Thus, children’s early concepts are based on prototypes of the objects and people they encounter person-ally.
They then decide if new objects are similar enough to the prototype to be a “Mommy,” a “cookie,” a “doggie,” and so on. Because proto-types may differ as a result of personal experi-ence, there is considerable room for arbitrariness and individual differences in prototypic concepts. Thus one person’s “terrorist” can be another per-son’s “freedom fighter.”
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How we state propositions can influence, how we try to solve a problem, reason through to a decision, or make a judgment. For example, in one study, college students who were told that a cancer treatment had a 50 per cent success rate judged the treatment to be significantly more effective and expressed a greater willingness to have it administered to a family member than did participants who were told that it had a 50 per cent failure rate.
Representing outcomes in terms of positives or negatives has this effect because people tend to assign greater costs to negative outcomes (such as losing $100) than they assign value to an equivalent positive outcome (finding $100). The proposition that “there is a 50 per cent chance of failure” evokes thoughts about the patient’s dying and causes the 50-50 treatment to appear riskier. Thus, differences in how we verbally represent choices and goals can make a difference in our perceptions and decisions.