Having shown the difficulty of establishing stable variation across varieties of English over the centuries, let us return to the distinction between transmission and diffusion of linguistic change made in 11.1. Social network analysis was used in this chapter to illustrate how these two principles come together and interact. Exposed to a wide range of linguistic variation and change, members of a mobile merchant network could select and promote certain practices and become linguistic intermediaries in a community. But they could also reproduce average usages of the language community at large, as was done by John Johnson, the ego of the Tudor merchant network studied in 11.2.2. Members of merchant networks were also locally grounded and had dense and multiplex ties in close-knit social networks. For example, where family and business combined, the master-apprentice relationship, for example, provided a context for transmission of linguistic change conducive to generational learning.
Historical sociolinguistic research may therefore not be easily reducible to the dichotomy of diffusion, understood as 'importation of elements from other systems', and transmission, defined strictly as 'linguistic descent' from parent to child (Labov 2007: 345-346). Labov himself (2007: 347) is well aware of the degree of idealization involved in these definitions: '[s]uch a clear dichotomy between transmission and diffusion is dependent on the concept of a speech community with well-defined limits, a common structural base, and a unified set of sociolinguistic norms'. This would typically be the case with close-knit social networks.
Although the notions of transmission and diffusion offer a useful conceptual distinction, in practice both of them are involved in real-time language changes. Making a distinction between primary and secondary diffusion, Joseph (2012: 421) relates the two as follows:
Successful transmission in part depends on primary diffusion, establishing lineal descent, and that sets the stage for possible secondary diffusion, which, in the usual case where there is no wholesale shift to another language (or dialect) but only the accretion of material from one into another, preserves lineal descent. Further, in its most usual sense, diffusion necessarily involves spread across different socially defined groups.
Combining the macro- and micro-levels, this perspective is key to understanding how real-time change progresses across the language community
over time and space and across social groups.