At least during your undergraduate studies, the nature of your writing assignments generally favors the active voice, because you usually write about general interest topics to educated laypeople and other scientists or engineers in a reader-friendly fashion. In general, a sentence that opens with a concrete simple subject followed by an active verb will serve you well; the rest of the sentence can reveal the new (and often necessarily wordy) information.
Two common circumstances follow where passive voice is too often used, even though active voice is completely practical:
- Generally, use active voice in the topic sentences and the opening sentences of paragraphs—that way the topic for the paragraph is clearly announced:
- When referring to another author’s work or introducing a figure or table, it is often stylish and interpretive to put the author’s name or the figure or table right into the subject of the sentence, then follow it with an active and literally correct verb:
Crustal rocks contain an interesting historical record. First, they reveal . . .
Batteries, inductors, and capacitors provide electrical energy storage. In batteries, high internal resistance allows for . . .
Feldman explains how the relative brightness of objects depends on the viewer’s angle of observation.
Figure 2 illustrates how fractal geometry can be used to create realistic landscapes.
The following excerpt from a meteorology paper demonstrates how admirable and efficient the active voice can be. This paragraph is especially impressive in that it explains the complex concept of vorticity through an analysis of the seemingly ordinary phenomenon of smoke rings. Note the consistent use of simple exact subjects followed by active descriptive verbs.
Figure 4 depicts a smoke ring in which the layers of a toroidal vortex ring are visible. As the picture shows, the smoke ring moves away from its source and trails smoke from its center. The trail of smoke behind the moving smoke ring indicates that the same viscous stress that caused the smoke ring to form also causes its eventual destruction. As the smoke ring continues to move (Figure 5), the outside boundary of the ring rotates toward the same direction as the relative motion of the surrounding air. The inside boundary rotates opposite in direction, and thus the change in relative velocity with distance across the boundary produces drag.
Clearly, this is a paragraph that the writer toiled over, yet, thanks to the clear transitions and sensible use of the active voice, it is highly readable and efficient. This writer understood well how to marshal active verbs to explain phenomena. Note how, thanks to the active verbs, we can readily picture the described phenomena even without the figures being supplied.
One cautionary note, though: even though you are generally allowed to use "I" (or "we") in papers written largely in the active voice, you must beware of overuse. Simple transition words can represent the writer’s thinking just as well as the use of "I." For instance, the word "apparently" can do the same job as "I believe that"; the word "however" is much better than "as I turn to another way of thinking about it." Also, using "I" can be distracting, especially because it might cause you to inject too much personal opinion or irrelevant subjectivity—technical papers are not the place to share digressive speculations or assert your personality. Remember that your focus is on information and your considered interpretation of that information. Strong interpretive verbs and confident, accurate pronouncements automatically suggest that an "I" is at work anyway, so concentrate on choosing simple transitions, concrete nouns, and muscular verbs.