110 Who Are Our Friends?
relationships with others. At the most basic level, individuals have a fundamental
need to belong, whose fulfillment is associated with numerous positive health,
adjustment, and well- being outcomes (Baumeister & Leary, 1995). Given the pri-
macy of this need, many general theories of motivation and need fulfillment (nearly
all) include relational need fulfillment for optimal well- being. For example, self-
determination theory (SDT) holds that it is individuals’ needs for autonomy, com-
petence, and, importantly, relatedness that motivate all of human behavior (Deci
& Ryan, 2000). Likewise, attachment theory (AT) holds that relational needs are
paramount for individual success, specifying in particular that the needs for caregiv-
ing, felt security, and sexual gratification are fundamental for individuals’ security
(Hazan & Shaver, 1987; Mikulincer & Shaver, 2003). Indeed, evidence gathered
based on both theories indicates that the fulfillment of relational needs (i.e., relat-
edness from SDT, and all three of the needs from AT) is associated not only with
higher- quality relationships (Simpson, 1990; Patrick, Knee, Canevello, & Lonsbary,
2007) but also with greater individual- level outcomes, such as overall psychological
health (Knee, Hadden, Porter, & Rodriguez, 2013).
Interdependence theory (IT) provides an account of need fulfillment that speaks
less to which needs individuals have that motivate their actions and more to the role
of need fulfillment in individuals’ lives (Rusbult & Van Lange, 2003). An inherently
dyadic theory, IT characterizes how relationship partners of all kinds can help each
other fulfill needs, and subsequently attain positive relationship and life outcomes
(Drigotas & Rusbult, 1992). From this perspective, it is assumed that individuals
have diverse sets of needs, some of which are pervasive, others of which are specific
to particular situations. Regardless of the exact needs, when a close other fulfills, or
helps to fulfill, needs, individuals are able to obtain the most important outcomes
derived from close relationships (Le & Agnew, 2001). Some of these outcomes
are concrete: the direct experience of pleasure and pain (Rusbult, 1980). Other
outcomes are symbolic: positive expectations regarding the trustworthiness and
dependability of the partner that arise from situations in which a partner’s prore-
lationship motivation can be discerned (i.e., diagnostic situations; Rusbult, 1980).
Both contribute positively to relationship outcomes, including satisfaction and
commitment within the relationship (VanderDrift & Agnew, 2012) and the experi-
ence of positive emotions (Le & Agnew, 2001).
From an interdependence point of view, then, many different relationship partners
can provide fulfillment of important relational needs. Friends, family, and romantic
partners, assuming the situation favors interdependence, can all be asked to meet
any of the needs individuals hold (with the exception of sexual needs being fulfilled
nearly exclusively within romantic relationships). This perspective is in line with SDT,
but stands in contrast to an attachment approach, in which a pair- bond is uniquely
suited for the fulfillment of attachment- relevant needs. We propose to reconcile this
discrepancy by suggesting that both AT and IT allow that certain situations are better
suited for particular needs, but absent that situation, individuals will still find venues