Active Voice – If a sentence is written using the active voice, the subject of the sentence performs the action expressed by the verb.
Passive Voice – If a sentence is written using the passive voice, an action is performed upon the subject of the sentence.
The active voice is generally preferred in academic writing, so it should be used throughout most essays. Using the active voice tends to make sentences more clear and less wordy. This becomes particularly important in longer sentences. Using the active voice allows for writing to be less wordy, and this makes for better writing.
There are exceptions when the passive voice is used, such as when the noun performing the action is obvious, unimportant, or unknown. This is because using the passive voice draws attention to the action itself rather than the noun performing the action. For instance, the passive voice is often used in scientific writing, such as in lab reports, where the emphasis is placed on the action.
Either way, all writers should be aware of the differences between the active voice and the passive voice and use the appropriate one for any given assignment. When in doubt, use the active voice.