Q&A for How to Understand the Difference Between Passive and Active Sentences

Use two versions of the same sentence as an example. For example, an active sentence could be "I threw the ball through the window," while a passive sentence could be "The ball was thrown through the window."

Passive. The subject (the key) did not directly do the unlocking. If the sentence was active, it would read "The key opened the lock."

Rarely in a natural construction. For example, you could rearrange the passive sentence "The cake was eaten by Beth" using inverted sentence structure (anastrophe) to get "By Beth the cake was eaten." Though not strictly incorrect, such a structure would very rarely be used in a natural conversational or written context, though you might find it in some types of poetry and perhaps religious texts. It's kind of a forced sentence type and most likely to be used either for a dramatic effect or to fit the flow/rhyme of a poem.

"The key opened the lock" is an active sentence.

It is written in active voice. That's because it's written in the form "subject (you) + verb (need) + object (to be...)" ("To be" is in this case a noun and so can be an object.) This is probably confusing. The main factor is the overall form of the sentence: subject, then verb, then object = active voice; object, then verb, then subject = passive voice.

A linking verb (a form of "to be") is neither active nor passive. Examples: "I am happy." "The boy was sad." "The girl will be glad to see you." "He cannot be there tonight." "I would have been angry if I'd known about it."

You have cited an imperative sentence (a command). Changing between passive and active involves only declarative and interrogative sentences.

The meaning is often the same in either case. Active voice is simply stronger and more direct than passive voice.

Even though the verb in this sentence is a "to be" verb ("is"), and therefore there's not much "action," the sentence is already in active voice: subject + verb + predicate adjective. (Also, because there's no direct object, the sentence cannot be changed to passive voice.)

Neither sentence is passive. In the first, the subject performs the action ("city will change"). In the second, there is no action at all. The subject is merely in a state of being: "it is."

It's passive, because the action (the altering) -- although not actually performed -- would have been performed upon the subject (the timetable).