What is the theme of Under the Greenwood Tree?

The story Under the Greenwood Tree is a pastoral romance by Thomas Hardy. It portrays the young romance between Dick Dewey and Fanny Day. There are several themes present in this work, but the prevailing one is Fanny’s desire for freedom and choice. Written in a time when the women’s suffrage movement was in full swing, Fanny represents choice and a turn towards modernity instead of the return to antiquity.
She falls in love with Dick, but her father believes him to be an unsuitable match and therefore prevents their marriage. However, they devise a plan to get around it and get engaged in secret. The next day, the vicar, who is a representation of the affluence and luxury of olden days, asks her to marry him. She briefly accepts. It is later revealed to the vicar that she had been engaged to Dick, and they call off their engagement. Eventually, she marries Dick without incident, portraying the step forward into women’s right to choice and to follow their own paths and lives—and not to be dictated by their fathers or by affluent suitors who can “pay the highest price.”

The theme of this novel is the way modernity clashes with—and ultimately refreshes—the old ways of life of the village of Mellstock. Fanny Day, the protagonist, is the symbol of modernity. She shocks the village, for instance, when she becomes part of the Mellstock choir, and when her organ, also representing modernity, is introduced into the choir.
She manages as well to make her own choice of a marriage mate, bringing her father around to the idea of her marrying the man she loves, Dick Dewey, who her father doesn't think is good enough for her. Foreshadowing the way the suffragists in England would get the vote in part by refusing to eat, Fanny refuses (or pretends to refuse) to take any food. And although she is temporarily tempted by a marriage offer from the high-status vicar, Mr. Maybold, like a modern woman, she opts to follow her own heart and stay with Dick.
The novel is a pastoral romance, meaning it is set in the country and depicts the world in an idealized way. In this idyll, modernity is not a threat but a boon to Mellstock.