The whole concept of internal monologue as a device is problematic for several reasons:
A) No one thinks in sentences. Putting your feelings / thoughts into language is the last step after they boil up from your personality / soul / brain.
B) It slows down the action because neither scene nor action nor interaction between characters are progressing while the IM character stops and thinks.
C) It makes the reader ask: well, if we can read his/her mind directly, why don't you just tell us and get it over with? Why didn't you just write a 1 paragraph essay instead of a short story / book?
D) It's telling, not dramatizing. This means that you have told us what the character is thinking rather than the character putting his thoughts into action (a la Aristotle, who said that all character is action, meaning that a change or thought within a character must be expressed in action or else it didn't really happen. If a character's inner life fell in the middle of the woods and no one was around to hear it, did it make a sound? Forrester and Smiley disagree with the concept that character must express itself in action and say that, indeed, thoughts and feelings not outwardly expressed are the measure of a round character.)
Rather than stopping the forward action of your story by having your characters do something like, I considered this, and I don't know what to do, You can use third person omniscient narrator to show us what she is thinking, for example, the excellent IM in Mansfield Park by Jane Austen, where the lazy Lady Bertram, who asks her husband whether she herself is hungry, she "did not think deeply, but, guided by Sir Thomas, she thought justly on all important points; and she saw, therefore, in all its enormity, what had happened, and neither endeavored herself, nor required Fanny to advise her, to think little of guilt and infamy."
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Author of RABID: A Novel and CALLOUS: A Novel
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