Someone locks the office every morning. The office is locked every morning. Someone has invited Sarah to the party. Sarah has been invited to the party. We use the passive when we are not interested in who or what does something The factory was painted during the war. Sarah has been invited to the party. I made a mistake. A mistake was made . We also use the passive when we do not want to say who or what does something Compare
I did this experiment several times. Each time I got the same results. After the last time, I was convinced that I was right. The new bacteria must have caused all the problems we found in our patients.
The procedure was repeated until there was certainty regarding the results. The problems encountered by the patients were caused by the bacteria.