Saylor.org's English Composition/Avoid “To Be” – Reaching for Colorful Verbs
Like passive verbs, forms of "to be" ("am," "is," "are," "was," "were," "be," and "been") are relatively weak verbs; they express a state of being instead of colorful action. "To be" seems to work in practically any sentence, but there are a variety of better, more interesting verbs that can take the place of the static verb "to be." Overusing "to be" verbs can be a way of telling instead of showing (e.g., "John was a fan of 40s music"), and using too many "to be" verbs can contribute to wordiness. Consider the difference, for example, between "be in favor of" and "support" or "be indicative" and "indicate." Reread some of your old writing with this in mind, and you suddenly may notice the repetitiveness of the use of "to be" verbs. When editing a paper, strive to notice any and all times a form of 'to be' is used and think of ways to re-write the sentence with a more interesting verb. Thesauruses are your friends. Compare these sentences:
The fireworks were bright and noisy. They were lighting up the night sky.
The fireworks exploded and boomed, lighting up the night sky.
Just like that, your writing becomes simpler, cleaner, less repetitive and more interesting.