antitheton

1. A proof or composition constructed of contraries.
Antitheton is closely related to and sometimes confused with the figure of speech that juxtaposes opposing terms, antithesis. However, it is more properly considered a figure of thought (=Topic of Invention: Contraries). (Silva Rhetoricae)

2. If a mode of expression both easy and adorned is desired, set aside all the techniques of the dignified style and recourse to means that are simple, but of a simplicity that does not shock the ear by its rudeness. Here are the rhetorical colours with which to adorn your style: (Vinsauf)

2. (Contentio) There are other figures to adorn the meaning of words. All of these I include in the following brief treatment: when meaning is adorned, this is the standard procedure. ... ((9) contentio) [by contentio] I institute a comparison in which the positions set forth are antithetical to each other. (Vinsauf)

1. Flattery hath pleasant beginnings, but the same hath very bitter endings. — R. Sherry (qtd. in Silva Rhetoricae)

2. He who was rich became poor; he who was happy, wretched; he who enjoyed such radiance was thrust back into darkness. (Vinsauf)

2. ((9) contentio (antithesis)) It may be that no mortal thing disturbs them, yet while this stands against them the death of the soul results from one sin as well as from many. (Vinsauf)