 When do we include by someone in a sentence in the passive voice from espressoenglish.net? When the person who did the action is completely unknown, we usually don't include by someone. For example, in the sentence, the bank was robbed. We don't need to say the bank was robbed by someone or the bank was robbed by robbers, because this doesn't add any interesting or relevant information to the sentence. Now, if we have some information about the bank robbers, we can include it. For example, the bank was robbed by five middle-aged white men. Even though we don't know the exact identity of the robbers, the phrase by five middle-aged white men adds extra and relevant information to the sentence, so we can include it. Now, when we do know who did the action, including by or not, depends. For example, if you're on a tour of India, the tour guide might say, the Taj Mahal was built by the Emperor Shah Jahan in memory of his wife. In this case, the phrase by the Emperor Shah Jahan adds some interesting extra information. If you're on a tour of New York City, the tour guide might say, the Empire State Building was built in 1929. He probably won't say by a construction company, because the phrase by a construction company is not very interesting or important. When you don't know who did the action, in general, don't include by someone in the passive voice sentence. And when you do know who did the action, you can include by someone if that detail is interesting or important. Thanks for watching English Tips from Espresso English. If you liked this video, please share it.