Metaphors evoke powerful images

A metaphor is also a comparison of one thing to another, but it differs from a simile in that it describes the thing being compared as if it actually were the other. For example, ''When it came to standing firm, he was the Rock of Gibraltar.'' The comparison can be made also by attributing characteristics or actions of one thing to another. ''In his resolve, he was solid as the Rock of Gibraltar.'' Here is an excerpt from a speech by a bank executive in which the financial markets are given the attributes of a life-support apparatus:

To one degree or another, the financial markets reflect just about everything that is occurring—or is expected to occur—throughout the world economy. As the economy's life-support system, they provide measures of the blood pressure, heart rate, brain waves, and general health of the system.

Sometimes an entire speech, or a large part of it, is built on a metaphor. An executive of a high-tech company concerned about an impending recession and growing competition from foreign producers of electronics began a speech by announcing that he would be speaking on herpetology, the study of snakes:

The snake I would like to talk about this morning is the boa constrictor. Now . . . some of you may have labored in the past under the impression that the boa constrictor drops out of a tree on its victims and quickly crushes them in the powerful folds of its body. That is not how it operates. On the contrary, extensive research on the part of my staff, which consisted of my secretary looking up ''boa constrictor'' in the Encyclopedia Americana, has revealed the true modus operandi of this dangerous reptile. Let me read it to you:

''Ordinarily the snake places two or three coils around the chest of its prey. Then, each time the victim relaxes and exhales its breath, the snake simply takes up the slack. After three or four breaths, there is no more slack. The prey quickly suffocates and is swallowed by the boa.''

This deadly phenomenon of a victim becoming a willing accomplice in its own destruction is not confined to the animal world.

The big boa we are facing—or rather failing to face—is the aggressive . . . hungry . . . efficient offshore competition, and each coil of the snake is another recession.

The speaker continues the boa-constrictor metaphor by talking about what happens when economic conditions improve and the industry breathes a sigh of relief. Then, he says, ''the boa constrictor smiles as we relax again.''

This metaphor creates some powerful images, especially the one of the boa smiling and tightening its grip. The boa metaphor slithers along for several paragraphs.

Unless you're trying for a laugh, be careful not to mix your metaphors. I once heard a CEO say, ''Our company is at a crossroads today, and we are going to have to navigate some stormy seas in the next few months.''