Killingsworth says that he "prefers the term trope to figure of speech because figures of speech are also figures of thought and figures of writing. Tropes help us to classify and study other functions of appeals. They suggest how one position (author, audience, or value) can relate to another"(Killingsworth 121) However, I was wondering about motifs. Are motifs types of tropes? Do motifs form tropes which form genres? The Bedford Glossary defines motif as a recurrent, unifying element in an artistic work, such as an image, symbol, character type, action, idea, object, or phrase. A given motif may be unique to a work, or it may appear in numerous works" (p.316). I think a motif is something symbolic that turns up recurrently in works to reinforce the main theme.
I was looking on the TV Tropes website in the motif section: http://tvtropes.org/pmwiki/pmwiki.php/Main/Motifs. For example, the Flower Motif says that "''Flowers are one of the most popular motifs in literature and television alike. Whether given as a gift, or mentioned as a character's favorite plant, they're probably worth taking note of; they may well be saying something about the story's theme or someone's personality. A character's flower garden will also give the audience an impression of their personality, usually in conjunction with the state of their house or personal appearance. A garden that is extremely well kept, but with little or no flowers in it, suggests an orderly but clinical personality; a garden overgrown with weeds might suggest a cynic who doesn't see the beauty in life any more, while a disorganized but thriving garden full of flowers probably belongs to a cheerful and badly-organized owner."
So are motifs just descriptive elements needed to create tropes? What I can say is that tropes are necessary plot devices.