Active voice is the subject in the sentences that performs an action while passive voice is the action performed upon the object of the sentence. If the sentence includes a prepositional phrase with the word 'by', it is most likely passive voice. While passive voice is permissible, too much passive voice will cloud an essay.
Let's talk about active and passive voice, now if you're anything like me, when I was in high school and I had teachers mark this on my paper, I had no clue what they were talking about and even better I had no clue how to fix it. So let's talk about what it actually is before we take a look at how we can work it in and correct it. So we've got Active and Passive Voice, when you speak in the active voice, what's happening is the subject is performing the action in your sentences, alright. "He kicked the ball" 'He' is our subject and he's performing the action right, he's kicking the ball. Passive voice though is when the action is performed on the object rather than having the subject perform it, so look at this sentence is passive voice "The ball was kicked by him" so now this object that we had up here has become the focus and it's being performed, alright. So it's not as clear what's going on or where the focus is. Now passive voice is not always the criminal, you can use it sometimes but let's take a look at why you might want to use active voice. Active voice is really nonscientific, it adds a lot of emotion to your writing, it's definitely much more clear and it helps you avoid wordiness. Look at the length of this sentence compared to the length of this sentence, you definitely saved yourself some words. So if you're somebody that's working under a word constraint and you're afraid you're going to go over, flip in to active voice is really going to be helpful for you. Now like I said, passive voice isn't always bad, when it's used sparingly, it can create an objective style because it takes the focus off the subject, so you can use it for that and then it's okay when the performer is either unknown or unimportant and we'll take a look at an example of that. But one thing to keep in mind is if you're consistently writing in passive voice, your writing is going to be cloudy, it's going to be wordy and it's not going to be easy to understand. So let's take a look at some ways that you can help identify when you're writing in active voice and when you're writing in passive voice, so the first trick is if your sentence includes a prepositional phrase with the word 'by' you probably have passive voice. Think about that first example, "the ball was kicked by him" so there is that example of how that's pulled in. Passive voice verbs also will always contain a 'to be' verb, so that's another thing to be on the lookout for. It doesn't mean that everytime you use a 'to be' verb, you're talking in passive voice, but it is one indicator that you might be there. So any time you see 'is, am, are, was, were or been' double check to see which voice you're speaking in. Let's take a look at some examples, alright. "The police were notified that there was a felon on the loose," alright, so we see this 'were' and that's our first clue that we actually are in passive voice, right? The police aren't actually performing any action there, we know that they were being notified and they probably be notified by somebody. So we've got passive voice but this is an example of when it's okay, really if we added "The police were notified by the dispatcher," that doesn't add much to our sentence, the identity of the dispatcher it doesn't really seem to be important, so this would be an example of when that, or the performer is unknown or unimportant, so you can kind of keep it there, alright. Now we have "The students passed the summer reading exam" is this active voice or passive voice? Well let's look at our subject, 'the students' are they actually performing an action? Yeah, they passed the exam so they're actually doing something, this is active voice, alright. The information you need will be presented by the teacher tomorrow, alright we've got a big indicator here that we're in passive voice. Remember we said the prepositional phrase that starts with the word 'by' and it's followed by an object is an indication that we might be in passive voice, and here we are because if we go to the subject, the information, it's not doing anything, there's no action there, alright. If we wanted to take this and transfer it into active voice, it would be pretty easy though, we can decide well who's actually doing something here. Well it's the teacher that's going to be presenting information, so let's focus here and change the sentence to "The teacher will be presenting the information you need tomorrow" now we've taken the same idea, flipped it from passive to active. Finally "I will sit by the oak tree" alright we've got that 'by' word again, so let's double check it, it is followed by an object there, but is this object doing anything in the sentence? No, in fact we have a subject up here 'I' and we have 'I' sitting by the tree, so this is actually an example of something that's inactive voice that does include that propositional phrase with the 'by' so don't always let it lead you down that passive path. So hopefully now you can differentiate between the two Active and Passive Voice, like I said passive is not always bad but you want to use it sparingly and now you've got some tricks for turning it into active voice when you're in passive voice.