be secondary . Maddi (1980), who reviewed the major types of personal -
ity theory , discussed individual differences in terms of what he calls pe -
ripheral characteristics, in contrast to the core characteristics that form
the heart of personality theory . Trait psychology would seem to be allperiphery and no core; why settle for that when other schools promiseboth?
The answer is, in part, because other schools are less than fully suc -
cessful in delivering a good model of individual differences. Each school
leads to an emphasis on certain characteristics, often to the exclusion ofothers. Freudian theory , for example, is primarily concerned with neu -
rosis and impulse control. It has an elaborate system for describing the
varieties and degrees of maladjustment. But it fails to say much of sig -
nificance on other individual differences, such as why some individuals
are introverted, some extraverted. Psychoanalysts might well claim that,from their point of view , differences on that dimension are trivial. Othertraits are trivial from other points of view. Only a system that grants thefirst place to individual differences will attempt to provide a compre-hensive list of traits. And comprehensiveness is essential if we are inter-ested in the area of personality and aging. How can we specify whatcharacteristics do and do not change unless we know the full range ofcharacteristics to look at?
Historically , trait models appear to be by-products of personality
theorizing. Wouldn’t it be possible to begin with traits and build up atheory of the whole personality system? That would provide the dy-namic context in which traits operate and should satisfy the need manypsychologists feel for a more process-oriented approach to personality .In recent years we have tried to do just that, by proposing a Five-FactorTheory of personality (FFT; McCrae & Costa, 1996, 1999). That theoryis based on trait research, and a description of FFT is best postponeduntil the findings have been presented. In the meantime, we can pro -
ceed with a purely phenotypic approach to traits.
BASIC PRINCIPLES OF TRAIT PSYCHOLOGY
In common speech, when asked to describe someone, we generally rely
on trait terms. We say that one person is hardworking and aggressive,another is hostile and unimaginative, a third is shy but loyal to friends.Learning how to use such words properly , as applied both to others and24 PERSONALITY IN ADULTHOOD