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The previous two chapters introduced the idea of traits and discussed interactions between situations and behaviour, and that behaviour, when aggregated across situations, provides evidence for the existence of traits. In addition, we saw that the basic structure of traits in different cultures (a special kind of situation) is, by and large, reliable and replicable. In this chapter, we discuss how personality develops over the life span, particularly with regard to traits. How stable are our personalities as we go from childhood to adulthood, and during adulthood? In this chapter, first, we discuss traits and their stability in adulthood. Second, we introduce the concept of temperament and its relationship to personality traits. Finally, we look at the evidence that childhood temperaments are related to adult personality traits.
For a trait to be valid, it must have a degree of stability over time. A quality that is shifting, or that depends on the situation at hand, cannot accurately predict behaviour during a future event (i.e., it cannot account for reliable variance in that event), nor can it have a stable biological basis in the individual. Without some stability of individual differences, the theory of traits fails in its entirety. As with other aspects of trait theory, the problem of demonstrating stability is a bit like pulling yourself up by your shoelaces: the demonstration of stability is best done using validated trait assessments.