Antithesis

Placing opposite ideas or words side by side, so that one lights up the other through contrast.

In Dom Casmurro

Imagine a grand design carried out with small means.

"Grand design" and "small means" stand in direct opposition, and the contrast measures what the narrator sees in Capitu: the size of the plan against the modesty of the resources she has at hand.

Chapters XIII to XXII: Capitu, the Wall, and the Plan, the narrator

she concealing with words what I published through silence

Chapters XXIII to XXXIV: The Gypsy Eyes and the Eyes of Undertow, the narrator

Capitu looked inward into herself, while I, in truth, stared at the floor

Chapters XLII to LIII: The Oath at the Well and the Departure, the narrator

Now I remembered everything that then seemed to me nothing.

Chapters CXXXVI to CXLVIII: The Cup, the Separation, and the Rest, the narrator