This chapter deconstructs and compares two English syntactic variables as case studies to explore the linguistic/social interface in variation. The two variables are: (1) complementizer alternation (that/Ø) and (2) subject relative pronoun alternation (who/that/Ø). While both are internally and externally conditioned, the nature and strength of the predictors (also known as factors) differ significantly. I argue that the results from quantitative linguistic analysis, statistical modelling and a comparative perspective grounded in social and historical context provide unique insight into the synergy of social, cognitive, stylistic and linguistic factors. In the case of complementizers, the overwhelming influence of verb is the linguistic footprint that a particular collocation (e.g. I think) has grammaticalized into an epistemic parenthetical away from the original matrix plus complement construction. In the case of relative pronouns, the preponderance of who for subject, animate antecedents aligns with a well-known typological pattern (i.e. human animates contrast with non-humans), which is overlain with social evaluation originating from its prestigious origins that endures in current usage in the speech community. In sum, interpreting the varying roles played by multiplex influences on linguistics features is key to understanding variation.

Life-span theory has long emphasized that cognitive functioning and well-being are key constituents of successful development and aging. There is mounting empirical evidence that these central domains of life are closely intertwined, with better performance on a number of cognitive ability tests going hand in hand with higher levels of well-being and satisfaction. Less well understood, however, are the multiple different sets of pathways that underlie how and why well-being either represents a consequence of cognitive functioning and development or operates as an antecedent condition thereof. The major objective of the current chapter is to provide a select overview of (1) an exemplary set of mechanisms that help explain the often dynamic and reciprocal links between the two major areas of life and (2) the role that several layers of individual and contextual factors play as resources and constraints. To do so, we proceed in four steps. First, we review conceptual considerations and empirical evidence on stability and change in well-being from mid adulthood to very old age, the vast individual differences in levels and rates of change, and how these differences are shaped by cognitive functioning and change. Second, we consider how well-being may serve as an antecedent of functioning and development of cognitive performance and abilities. Third, we present stress reactivity, health behaviors, social participation, and neurological pathways as some of the presumed underlying processes. Finally, we discuss the role that resources and constraints at individual and contextual levels may play for linking cognition and well-being.