Monologues

What does it take for someone to play a monologue? A recent review by a friend prompted me to think about this.

Depending on the book, it seems like a display of schizophrenia on stage. How do you appear convincing switching between roles? It's difficult to get into character for each since you have to be mindful about switching roles during the act. So the actor will need a certain amount of tenacity.

I can't help but think of Emily of Emerald Hill, a rather well-known local monologue play. Margaret Chan did a pretty good job (I've not seen others, but will catch the Ivan Heng's portrayal that's showing next year). I realised that it was essentially playing the same character, except at different stages of Emily's life. The audience needs to "transport" themselves along with the character. So does this makes it easier? A single character portrayal?

I believe the book plays a part too. You need a defining characteristic of each persona, which will need to be drawn from the book. So the actor will need to pick out that defining characteristic to emphasize, and use it to his/her advantage so that the audience can tell when the actor switches.