  We investigate mechanisms for language change within a framework where an
unconventional signal for a meaning is first innovated, and then subsequently
propagated through a speech community to replace the existing convention. We
appeal to the notion of universality as it applies to complex interacting
systems in the physical sciences and which establishes a link between generic
('universal') patterns at the macroscopic scale and relates them to symmetries
at the microscopic scale. By relating the presence and absence of specific
symmetries to fundamentally distinct mechanisms for language change at the
level of individual speakers and speech acts, we are able to draw conclusions
about which of these underlying mechanisms are most likely to be responsible
for the changes that actually occur. Since these mechanisms are typically
believed to be common to all speakers in all speech communities, this provides
a means to relate universals in individual behaviour to language universals.
