I am taking a look yet again at my first novel, Fatal Score (initially called Hack the Yak), which I am preparing to query. I asked an editor to look at the first three chapters. The results were eye-opening.
When I began writing, I used interior monolog (protagonist’s thoughts), which I laid down in italics. The editor would have none of that.
I’ve mentioned before that the Big Duh I’ve learned by writing, now, three novels: there is this thing called technique. The writer needs that ineffable quality known as Voice, to be sure. And Mechanics (grammar, lexical sophistication, punctuation) must be spot-on or 
any self-respecting agent will trash the ms without reading it. The Big Duh was this thing I call Technique. Frustrating, is technique (in Yoda’s words). Some parts are common sense (when they become obvious), like letting a reader know where she is, who is speaking and what time it is at the beginning of a scene. Some parts seem like a random variable extending over time. Nineteenth-century technique (never mind punctuation) is different than twenty-first century for no apparent reason. Eighteenth century writing embraced long, Latinate words; Hemingway didn’t.
So, I live and continue to learn.
And, yes, I dumped most of the italics.
Son of a gun. I’ve been using italics for internal dialog, too, and my editor allowed it in Pumping Sunshine. Too late now to change them. I did, however, choose a font (Constantia) whose italics are easy to read.
Susie,
Thanks for your note. I think the italics work fine in Pumping Sunshine. The editor commented, “Careful with internal narrative. It’s lazy writing and jars the reader out of the story. One moment we are in third person and the next we are in first person POV.” Fatal Score is close third person, so internal monolog is a POV switch to first person. You’re in first person all the way.
Whether it’s first person or third person “limited” narration, quotation marks should be enough to differentiate thoughts from speech. If it’s omniscient, then it probably needs a “he/she thought” with no quotation marks. On the other hand, a specific device, like italics for interior monologues, if used consistently, should not necessarily damn the work. This may be as much an aesthetic quirk of the editor as it is the author.
Although you are certainly correct that writing styles have changed since the 19th century writers, I am not convinced that they have necessarily improved.
I love this thinly disguised self-assessment by Nathaniel Hawthorne in his introduction to his short story, “Rappaccini’s Daughter,” in which he is describing the “fictional” author, M. de l’Aubepine, whose titles in French very much resemble several of Hawthorne’s own creations:
“As a writer, he seems to occupy an unfortunate position between the Transcendentalists (who, under one name or another, have their share in all the current literature of the world) and the great body of pen-and-ink men who address the intellect and sympathies of the multitude. If not too refined, at all events too remote, too shadowy, and unsubstantial in his modes of development to suit the taste of the latter class, and yet too popular to satisfy the spiritual or metaphysical requisitions of the former, he must necessarily find himself without an audience, except here and there an individual or possibly an isolated clique.
Ah, yes, there is that. If we cut genres too thin to fry, we may end up with an audience of zero. Great comment on inner monolog. I will add it to the back-burner soup my critique friends are cooking up.