Paul saw his parents as 'only polarites', How does Goldsworthy use polarites in his construction of the novel?

The voice of the older Paul interrupts to comment that as he sets down his initial negative memories of Keller, it seemed—and still seems—impossible that he would come to love his instructor as much as he did. He returns to the story, criticizing Keller to his parents and calling him a Nazi, to a harsh reaction from his father. Afterward his mother reminds Paul how important it is to his father that he study piano, as his father regrets that the War prevented him from becoming a better pianist. Paul describes the polarity of his parents—his tall, stoic, quiet father and short, emotional, talkative mother who disagreed on everything in a half-serious, half-teasing way, except for music, the true career for the Government Medical Officer and librarian-turned-housewife.