In an active voice, the subject is doing the action. In a passive voice, the target of the action gets promoted to the subject position. Hope this helped.
Examples would probably help: Active: Bob read the book. Passive: The book was read by Bob. Active: On opening night, the play's director thanked the actors for all their hard work. Passive: On opening night, the actors were thanked for all their hard work by the play's director. Hope this helps!
Exactly. It's also worth mentioning that the agent performing the action can get dropped completely: The book was read. On opening night, the actors were thanked for all their hard work. (The originals were "long passives", and my versions are "short passives"). It's important that the active and passive voices are all about whether the agent performing the action is the subject of the sentence or not. Some sentences can have structures very like the passive voice but not be passive at all: The book was boring. On opening night, the actors were nervous.
There are times when passive voice is what you want. Maybe you don't wish to emphasize or even identify who is performing an action. Other times you may want to keep a passive tone to heighten the impact of an upcoming passage in active voice. In general, active voice makes for stronger writing. Subject and verb take center stage, and the action shines forth. But you should master both, and use each for its strengths.
As Cog said, both have their uses. On some forums passive voice seems to get a bad rap and one could get the impression that any use of passive voice makes for weak writing. Untrue. Often, it is appropriate and should be used when such is the case.
Absolutely. It might be worth mentioning that the short passive -- where the agent has vanished completely -- is particularly used by officials who don't want to admit responsibility. They don't say "we made mistakes", they say "mistakes were made". And sometimes the agent isn't known. "The train was delayed." Who delayed it? The driver? Engineering works? Vandals? The speaker doesn't know, they just know that the train was delayed, so passive voice is appropriate (although the speaker could say "the train was late", which isn't passive). But the basic rule is that active doesn't have to be justified, but you need a reason to use the passive.
incidentally, margaret atwood is credited with having written a work entirely in the passive voice that wasn't completely boring, but rather, excellent.
One thing to note: in terms of Linguistics, there is nothing inherently bad about passive voice per se. It's just another way of expressing a statement, with different emphases; after all, if it really was inherently 'weak', it probably wouldn't be used as much anyways, if at all. However, in our current culture of language or whatever you want to call it, passive voice is not something that is well-received and is generally perceived as 'weak', so you shouldn't overuse it, and be careful when it does appear in your writing. Another thing: It's important to note that just because "be", "am", "was", etc., are preceding a verb, does not mean that it's passive voice! A lot of people, even professionals and academics, make this mistake. For instance, the sentences "It was raining" and "I am eating" are NOT in passive voice; instead, the bolded words in this case indicate the progressive aspect. Unfortunately I don't know whether this is also not well-received in writing in general (and if someone can enlighten me, then please do so!), but I think it is pretty important to make the distinction nevertheless.
