148 II. BIOLOGICAL  FOuNDATIONS
A Structural Model 
for Studying  Temperament
A major factor that facilitated the aforemen -
tioned convergence of most (though defi -
nitely not all; see Block, 1995) personolo -
gists on a consensual, phenotypic taxonomy 
was the recognition that personality traits 
are ordered hierarchically, so that there is no 
fundamental incompatibility between mod -
els emphasizing a few general “superfactors” 
and those that include a much larger number 
of narrower traits (see Markon et al., 2005). 
At the apex of this hierarchy are “the Big 
Two,”1 originally dubbed simply “alpha” and 
“beta” (Digman, 1997), but later cogently 
interpreted as stability and plasticity (De -
Young, Peterson, & Higgins, 2002). At the 
next level, alpha (stability) decomposes into 
distinctive dimensions of negative emotion -
ality (or affectivity or temperament; Watson 
& Clark, 1984) and disinhibition (vs. con -
straint; Watson & Clark, 1993), with beta 
(plasticity) at this level typically focused on 
positive emotionality (or affectivity or tem -
perament; Watson & Clark, 1997), thereby 
reflecting the well-known Big Three model 
of personality (e.g., Eysenck & Eysenck, 
1975; Gough, 1987; Tellegen, 1985). Dis -
inhibition then splits into two dimensions: 
disagreeable disinhibition (i.e., low agree -
ableness [A] of the five-  factor model; FFM) 
and unconscientious disinhibition (i.e., low 
conscientiousness [C]). Finally, at the five- 
factor level, beta/positive emotionality splits 
to form separate extraversion/positive emo -
tionality and openness factors, which yields 
the familiar FFM (e.g., Digman, 1990; Mc -
Crae & Costa, 1987, 1997). Thus, the major 
higher order traditions within personality— 
including the Big Two, the Big Three, and 
the Big Five—all can be organized into a 
common multilevel structure, effectively ad -
dressing Revelle’s (2008) lament that, unlike 
intelligence, “unfortunately, . . . hierarchical 
models are not common in the non-  cognitive 
domains of personality” (p. 520).
More recently, researchers have begun to 
explore the levels of personality below the 
Big Five, which each can be divided into 
several distinct, yet correlated, traits. For 
instance, the general trait of extraversion 
can be subdivided into two aspects  variously 
called enthusiasm and assertiveness (De -Young, Quilty, & Peterson, 2007) or com -
munal and agentic extraversion (Watson, 
Ellickson-  Larew, et al., 2019). Then come 
the better known and more specific facets,  
of which three, in the case of extraversion, 
show the greatest convergent validity (though 
there is not strong consensus on their labels): 
assertiveness/ascendance, gregariousness/so -
ciability/affiliation, and positive emotions/
positive emotionality/positive temperament/
energy/activity/liveliness (Costa & McCrae, 
1992; Depue & Collins, 1999; Lee & Ash -
ton, 2004; Soto & John, 2009, 2017; Wat -
son & Clark, 1997; Watson, Nus, & Wu, 
2019; Watson, Stasik, Ellickson-  Larew, & 
Stanton, 2015). Facets are followed by even 
narrower traits, called nuances,  which are 
essentially items or small groups of items 
called HICs (homogeneous item compos -
ites) (Mõttus, Kandler, Bleidorn, Riemann, 
& McCrae, 2017; Mõttus et al., 2018); and, 
finally, specific behaviors (Digman, 1997).
The “Big Three” as a Structural Framework 
for Temperament
Although all levels (at least down to that of 
facets) need to be considered in a compre -
hensive assessment of personality, we focus 
primarily on the broad, higher-  order three- 
factor level for several interrelated reasons. 
First, the available data are most extensive 
at this level of the hierarchy, particularly for 
neuroticism and extraversion, which appear 
in every major structural model of person -
ality. For instance, there is much more evi -
dence regarding the genetic basis (Vukasovi ć 
& Bratko, 2015) and biological substrates 
(e.g., De  Young, 2010; Chapter 8, this vol -
ume) of extraversion and neuroticism than 
of other traits (although data on the level of 
the “Big Five” traits are increasing; see De -
Young, 2010).
Second, there currently is much better 
consensus regarding the three-  factor level 
as reflecting dimensions of temperament  
compared to the broader construct of per -
sonality, which incorporates both more in -
terpersonal and cognitive characteristics, as 
found in agreeableness and conscientious -
ness, respectively, at lower levels of the hier -
archy. Moreover, researchers within the Big 
Three tradition—  plus the overlapping rein -
forcement sensitivity theory of Jeffrey Gray 