Hints on English. Simple technical English should be used, and reports are written in the third person impersonal, past tense. Engineering and trade terms should be used, but the style should be dignified, though not necessarily formal. [...] Few persons can compose a report at the typewriter and use the best English.

The above quote describes a convention that's been passed down from generation to generation of engineers, almost to the point where young engineers reach the workforce writing this way instinctively. One of the principal features of that convention is the passive voice: "...reports are written in the third person impersonal, past tense."

When you use the passive voice, the object of an action becomes the subject of the sentence. In the above case, "reports are written." The active voice, on the other hand, places those performing the action as the subject.

Passive voice:
"Reports are written in the third person impersonal."

Active voice:
"You will write reports in the third person impersonal."
"We write reports in the third person impersonal."
"Write reports in the third person impersonal."

...and so on. Notice the characteristics of instructions written in the passive voice:

• You can't assign responsibility for a statement. Does the instruction come from God, Time, Fate, or Whatever (GTFW)? Is it performed by magic?
• Readers must perform extra work to figure out what's going on in the statement.
• Its truth is assumed to be unquestioned.
• Its authority level is imposing. Which is certainly true if it comes from GTFW. But what if it doesn't?
• Trivial details are magnified. As is the case with the use of "engineering and trade terms" above. How can we as engineers avoid using them?
• Sentences are longer in general.

This is all to say that the active voice is what you need if you want to assign responsibility for an action, write in shorter sentences, and be more easily understood -- in general. There are times, however, when you still want the passive voice:

• To avoid assigning personal blame when something goes wrong.
• To soften bad news.
• To give emphasis to the object of an action.
• To deemphasize long subjects, or subjects that have to be defined.

Assignments

Rewrite the following example from Porter's paper, using the active voice:

It has been decided that, effective immediately, the doors to the plant will be locked at 9:00 AM each day. Only those employees who have been issued a special pass will be permitted to enter thereafter. All others will not be admitted, and will be docked the day's pay.

Is this memo clearer in the active voice? What information is still needed to make it fully informative?

References

Porter, K. "Usage of the Passive Voice." Technical Communication, First Quarter 1991.
Rew, L. J. Introduction to Technical Writing. NYC: St. Martin's Press, 1993. ISBN 0-31206-781-X