As this excellent answer points out, the passive voice can change the emphasis of a sentence from the subject to an object. That seems to be its primary function: this other answer provides an example of how the passive voice is used in academia to draw emphasis away from the author of a paper and towards the paper's findings. However, are there any effects of using the passive voice other than changing the focus of the sentence? If so, what are they?
A couple of thoughts:
- It allows one to avoid awkward constructions in some cases:
The canyon was worn smooth by glaciers, water, wind, centuries of foot traffic, and now the grading machine making its way down the center.
is better than
Glaciers, water, wind, centuries of foot traffic, and now the grading machine making its way down the center, wore the canyon smooth.
- Closely related to the change of emphasis, it is commonly used as a way of weaseling out of responsibility:
Honey, the kids got lost.
as opposed to
Honey, I lost the kids.
JeffSahol is right but it's not only about 'weaseling out of responsibility'. It's generally a perfect way to omit information, which is obvious or of no importance.
The system is to be parameterized as follows.
But by whom? Well, it doesn't matter by whom. It just has to be done. (Sorry, passive voice again.) Why should I put the sentence into the active voice and invent an actor (you, the user, the administrator)?
The report is printed automatically twice a day.
Is there anybody out there who doesn't know who/what prints the report? Do I, again, have to invent an actor (the printer, the system)?
If you look into a German instruction manual you'll see that it overflows with the passive voice - exactly because you can save your feather/fingers from producing unnecessary information. (Of course, it's also well-established in the German way of thinking.) I know what I'm saying because I'm currently translating such a thing into English. I'm meanwhile pretty sick of inventing actors just in order to please my word processing - a real passive voice hater - and, thus, allegedly the English-speaking customers.
A thoughful aside: I've read a couple of times the opinion that the passive voice is avoided because it's more difficult to grasp. Seriously? Are challenges considered bad? (Sorry, it's happened to me again.) Do writers acitvely participate in maintaining the people's low level of perceptivity? That would be sad.