* Time: Acts are often used to mark the passage of time in a play. For example, the first act might take place in the morning, the second act in the afternoon, and the third act in the evening.
* Location: Acts can also be used to mark changes in location. For example, the first act might take place in a living room, the second act in a forest, and the third act in a castle.
* Plot: Acts can also be used to mark major turning points in the plot of a play. For example, the first act might introduce the main characters and set up the conflict, the second act might develop the conflict, and the third act might resolve the conflict.
* Character development: Acts can also be used to mark changes in the characters of the play. For example, the first act might introduce the characters as they are at the beginning of the play, the second act might show them changing as they deal with the conflict, and the third act might show them as they have changed by the end of the play.
Ultimately, the criteria for dividing a play into acts is up to the playwright. There is no right or wrong way to do it, and the best approach will vary depending on the individual play.