'Passive voice' is possibly one of the most misunderstood issues in the mechanics of writing. I've seen it get confused with 'showing not telling', deep point of view, dynamic v static verbs and use of adverbs. Most often, though, I've seen it confused with use of the verb 'to be'.

All these issues are important for writers to understand, and I'd like, at some point, to mention all of them. However, this article is going to deal with just two things: defining passive voice and using the verb 'to be' - two separate, but related, issues.

Issue One - Passive v Active Voice:

On a writing site, I once saw this sentence labelled as 'passive voice':

She was climbing the stairs.

The suggested remedy, to turn it into 'active voice', was:

She climbed the stairs.

This is entirely incorrect. Both these sentences are active voice. The first is past continuous tense, the second past simple tense - that's all. Passive voice would be rendered thus:

The stairs were being climbed by her. OR The stairs were climbed by her.

The writer of this advice has made the (depressingly common) mistake of thinking that the inclusion of the verb 'to be' (in this case, 'was') makes a sentence into passive voice.

It doesn't. Passive voice is a specific construction whereby the subject of the sentence has something done to it rather than doing something.

Active voice: She hit me.
Passive voice: I was hit by her.

Active voice: I carried the baskets into the house.
Passive voice: The baskets were carried into the house.

Yes, in these examples, the passive voice sentences have the verb 'to be', but this is not what makes them passive.

Active voice: Goldilocks slept on the bed.
Active voice: Goldilocks was sleeping on the bed.
Active voice: Goldilocks was asleep on the bed.
Passive voice: The bed was slept on by Goldilocks.
Passive voice: The bed was being slept on by Goldilocks.

Issue Two - The Verb 'To Be':

Generally, as you can tell from the 'active voice' examples above, the sentences which eliminate the verb 'was' are shorter and crisper. Often, this can be a good thing.

Lucy was standing on the balcony to watch him leave.

is a little clunkier than

Lucy stood on the balcony to watch him leave.

However, the sense is slightly different for each sentence. If all you're doing is setting the scene at the beginning of a chapter, then this doesn't much matter either way, and you might as well use the slightly shorter sentence. But look at these next sentences.

Lucy was standing on the balcony when she heard a scream.
Lucy stood on the balcony when she heard a scream.

In the first sentence (past continuous tense), Lucy is clearly standing on the balcony to start with, then she hears a scream.
In the second sentence, the meaning is unclear. It could be read as any of these options:

When Lucy heard a scream she stood up on the balcony.
When Lucy heard a scream she went out to stand on the balcony.
Lucy was already standing on the balcony when she heard a scream.

Cutting out 'was' can - sometimes - be a good thing to do, but never ever ever if it makes your sentence ambiguous.

And not if it makes your sentence into a fragment, either. A fragment is an incomplete sentence - a sentence without a noun or without a verb, for instance.

Take these sentences:

Lucy looked up. She was clearly afraid.

Elsewhere on the net, I've seen this type of sentence revised, in order to get rid of 'was', thus:

Lucy looked up. Clearly afraid.

The second sentence is now missing a verb; it's become a sentence fragment. Although strictly ungrammatical, sentence fragments can be fine in fiction. They're short, crisp, have impact and can be used for very effective dramatic effect. But oh please, in moderation.

If you get rid of every instance of past continuous tense and turn all your 'was' sentences into sentence fragments, your writing might be safe from passive voice construction, but it's not necessarily going to be good writing. It's going to run the risk of being ambiguous, choppy and difficult to read.