Ivan Ilych possessed this capacity to separate his real life from the official side of affairs and not mix the two, in the highest degree, and by long practice and natural aptitude had brought it to such a pitch that sometimes, in the manner of a virtuoso, he would even allow himself to let the human and official relations mingle.
There are no more uses of "aptitude" in the book.
Show samples from other sources
Hyde’s study indicates that girls and boys have the same aptitude for math.
Evidently she had great natural aptitude for her work.