Interior monologue is the expression of a character’s thoughts, feelings, and impressions in a narrative. It is much like the internal monologue that runs through all our heads pretty much every waking second of every day. (Though writers should only share the thoughts that are relevant to the story!)
Writing interior monologue can be difficult to do well. You may be tempted to use trigger words and phrases like “I wondered,” “he thought,” and “she felt like” to express your point of view character’s internal monologue. You may also be tempted to use quotation marks around the character’s thoughts or italicize the font to show that the words are being expressed inside the character’s head rather than with her physical voice. However, if you use these tactics regularly, you should probably stop!
First, these types of trigger words and phrases can sometimes – well, often – tip you off that you are telling rather than showing. When you use these, ask yourself if you can show what the character is feeling or thinking rather than telling. Not only that, but telling that the reader wondered something, especially when writing in first person or third person limited, is redundant. We already know that the thoughts belong to the narrator, who is also the protagonist. Sometimes you can fix this by simply deleting the “I wondered” phrase.
Quotation marks should only be used to indicate that a character is speaking aloud. Thus, they simply cannot be used to express interior monologue. Not only is this bad form, but it is also bad grammar.
Italicizing your font to highlight the POV character’s thoughts isn’t much better. Italics can be hard on the eyes, especially in large chunks of text, and should be avoided at all cost. Before you decide to italicize anything, always stop and ask yourself why you need it and if there is a better way to do it.