Book titles–and newspaper and magazine headlines–are usually formatted in one of two styles: “up style” and “down style.”
This style calls for capitalizing the first and last words in the title or headline and all “major words” in the title.
Not all style guides agree as to what should be considered a major word.
Most agree that nouns, pronouns, adjectives, verbs, adverbs, and subordinating conjunctions (if, because, as, that, etc.) are major words and should always be capitalized. That leaves articles (a, an, the), prepositions, and coordinating conjunctions (and, but, or, for, nor) in the minor league where lowercase prevails. Unfortunately, as is frequent with arbitrary rules, style guides don’t always agree.
Both the Chicago Manual of Style and the AP Stylebook agree that articles (a, an, the), and coordinating conjunctions (and, but, or, for, nor) should not be capitalized unless they are the first or last word of the title, but when it comes to prepositions, they differ.
CMOS says never capitalize a preposition unless it is the first word in the title. AP says leave short prepositions in lowercase, but capitalize prepositions and conjunctions of four or more letters.
Here is how the same title would be formatted according to CMOS and AP:
CMOS: Four Theories concerning the Gospel according to Matthew
AP: Four Theories Concerning the Gospel According to Matthew
Most stylebooks state that all verbs are capitalized, including is, am, and be, but that the to of an infinitive is to be treated like a preposition and put in lowercase: How to Train Your Dragon, How to Be a Better Parent.
The only words capitalized in down style are the first word of the title and any proper nouns that appear in the title:
Four theories concerning the Gospel according to Matthew. (book title)
Coastal Commission enters fray over San Mateo County beach access (headline)
Down style has been adopted by many newspapers because it calls for fewer rules.
The purpose of having style guides is to make reading pleasant by providing a clear, consistent manner of presenting written material. If you write for yourself, adopt any style you wish for your blog or other publications. If you write for hire, follow your employer’s house style.
The following headlines and book titles taken at random from the Web illustrate the fact that not everyone follows the same stylebook:
Journey Home Finally Begins for the Victims of Malaysia Airlines Flight (headline, NYTimes)
Why Triumphant Jihadis In Iraq Will Help Assad Crush Opposition In Aleppo (headline, HuffPost)
Modern Identity Changer: How To Create And Use A New Identity For Privacy And Personal Freedom (book listed on Amazon)
Gone With The Wind (AMC filmsite.org)
Gone with the Wind (Imdb)
Gone With the Wind (Rotten Tomatoes)
Hardball: How Politics Is Played, Told by One Who Knows the Game (book listed on Amazon)
How To Hide Anything (book listed on Amazon)
Why Government Fails So Often: And How It Can Do Better (book listed on Amazon)
I’ll save the question of “Italics or Quotation Marks?” for another post on book titles.