Changing from first to third person
Question: As a general rule, does a fiction book seem strange if chapter by chapter, it changes from first to third person. How about when it's made clear that the change is occurring? Also, is it especially odd if the first person is present tense (I am, I do), and the third person is past tense (He was, he did)?Answer:
It is far more common to see books where the point of view switches from one character to another.
The big question you should answer in your mind is why these changes occur.
For example, Margaret Atwood's novel The Edible Woman
switches from first person to third when the main character feels she is losing her identity. It returns to first person when she regains her sense of self.
If you have a legitimate reason why parts of the story are told from the point of view of an external storyteller for whom the events are in the past while other parts are told from the main character's perspective for whom the events are unfolding in the present -- and if the changes in perspective add something to the story -- then fine.
Just remember that the cost may be that the changes are little disconcerting to many readers.
You may lose a little intimacy in 3rd person, but gain a slightly broader perspective.
You have to balance the costs and rewards and make the call -- or perhaps show the manuscript to people you trust and get their feedback.