Both metaphors and similes are examples of figurative language, language that is not intended to be interpreted literally. Both metaphors and similes can be very effective tools for conveying meaning and for enriching the images in your poetry. You are using a metaphor when you say that one thing is another. You transfer the qualities of the one to the other. You are using a simile when you say that one thing is like (or as) another. Again, you transfer the qualities of the one to the other. The metaphor is usually considered the stronger use of figurative language, as it promotes an identity instead of a comparison. Thus, the metaphor has the ability to go beyond the mere transferring of qualities to become a symbol.
While a metaphor or a simile can appear in a poem to enrich a single image or a thought or a line of verse, the use of the extended metaphor or extended simile into a controlling image, wields much more power. In the controlling image poem, the writer is writing on two levels simultaneously throughout the poem. This requires greater insight into the metaphor or simile and its application to the subject of the poem. It is very enjoyable to read, as the reader is engaged in the word/thought/image game to a greater degree than he would be for an occasional metaphor or simile.
To write a controlling image poem, the writer must marry as perfectly as possible his underlying comments about life (the theme or content) with his chosen controlling metaphor or simile. The controlling image must be appropriate to the content of the poem. If the controlling image is humorous, for example, it will not marry well to a theme that is serious. The result of such a union is a feeling of confusion or dissatisfaction for the reader. It will seem stilted, unthought, weak, or incongruous. The same is true for a serious metaphor joined to a trite or humorous theme. Sometimes an author may deliberately join such misfits to create the humor of incongruity, but such unions should be avoided unless that is the author's intent.
To find compatible themes and controlling images, the author will most likely start with one, then seek for the other. He may start with a theme and seek for an appropriate controlling image, or he may start with the controlling image and seek for some theme that is congruous to that image. Either way, the result is a marriage that is delightful for the reader.
For example, the author may note that some people who do not seem to fit in to a given group because they are different, are discarded by that group, thrown away in much the same way someone would haul trash to the curb, or pull weeds from a garden. The poem would adopt the controlling image of a trash hauler removing from a neighborhood the unwanted refuse, or of a gardener pulling and discarding or burning weeds from his vegetables or flowers. The writer would deliberately marry that controlling image to the idea of unwanted people, calling the unwanted people "refuse" or "weeds."
Read the following controlling image poem:
It is clear that the poem is being written on two levels simultaneously:
The controlling image of a tree loosing all its leaves deepens our understanding of this woman losing all her thoughts and memories.