In this sense, they are like the unmentioned premises in abbreviated reasoning, which can go unmentioned because they can be taken for granted as generally acknowledged.
Among the annoying challenges facing the middle class is one that will probably go unmentioned in the next presidential campaign: What happens when the robots come for their jobs?
With such generalizations taken for granted, the persuader can go immediately from a particular instance, one that falls under the assumed and unmentioned generalization, to the conclusion that the applicable generalization entails.
Emma accepted it with a very eager hand, with an impatience all alive to know what he would say about it, and not at all checked by hearing that her friend was unmentioned.
Having praised the zeal and competence of the Russian crew, he wrote: Neither can I leave unmentioned the readiness of the Japanese to give us all assistance and to supply us with all we needed.