Some writers put a modifier in parentheses
to inject their opinion or offhandedly highlight something about what's
being modified.
Two scraggly fifteen-foot palm trees in white trashcan
planters have been brought in for the occasion with the (unsuccessful)
idea of a festive touch.
Consider this without the parentheses or without
unsuccessful. The idea of a festive touch suddenly becomes
the UNSUCCESSFUL idea, with the aside far noisier than
a mere modifier.
Durkheim offered an even more specific (and more
dynamic) and less crystallized concept that is also a nonmaterial
social fact-social currents.
Naturally, the anti-smoking ideology presumes (wrongly)
that both conditions are true.
Like Chelsea [Clinton], they actually seem to
like their dysfunctional parents. Unlike her, they don't know (or
care) much about politics, and their main civic passions are
local: jobs, families, and community.