the most various of the rhetorical tropes, is the substitution of one word for another when the objects are related as causes, effects, or adjuncts. Thus, in the phrase, "To bring down one's gray hairs with sorrow to the grave," the effect is put for the cause; gray hairs are put for old age. We employ the same figure when we use the author for his writings, the inventor for his invention, &c. This trope was included by Aristotle under the general term metaphor.**