There's a black art to titles. Some of them have it, some of them don't. "What's 'It'--aside from a Stephen King novel?" you ask. "It" is that thing that makes you notice. The thing that makes you pick up a book and look at the back cover. The thing that makes a title to a book you've never read or a movie you've never seen stick in your mind, even though you don't care at all about the thing it's attached to.
There's a word for "it."
Emotional resonance is that thing that makes us look at a book title and go "oh!" (or "oh?" or "ah" or "huh?"). A title with immediate resonance requires no thought--it jumps down below our conscious minds and evokes something before we know what it's doing. Here are some titles that tap into something specific in our cultural atmosphere:
Soulless by Gail Carriger: The title contrasts with the subtitle ("A novel of Vampires, Werewolves, and Parasols") to subvert the connotation of "soulless" as being something negative and monstrous, but not entirely. It creates enough ambiguity that it makes us interested. Ambiguity that lures (rather than confuses) is good--it's one of the basic elements of seduction.
The Pillars Of The Earth by Ken Follet: A title which is actually a quote from 1 Samuel 2:8, a Bible verse that almost nobody has heard in a couple generations--but which was a favorite a couple hundred years ago. So much so that the image of eternity and strength becomes tied to this phrase in our language. Even though the cosmology (flat earth as the center layer in a layer-cake universe) is now completely alien, the phrase still evokes the sense of permanence and imperiousness that it did to its original audience. It is, to borrow another ancient image, titanic. And it works so well that it's helped Follett's book become one of the bestselling books of all time.
A Dark And Hungry God Arises by Stephen R. Donaldson: You gotta hand it to him, Donaldson knew his audience--this is the third book in a five-book space opera based on the Ring Cycle and steeped in Wagnerian and Lovecraftian imagery, and anyone vaguely familiar with Lovecraft will feel the echo of Cthulu in this title. Both of these mythoses serve (throughout The Gap Cycle) as a veneer over a plot which is centrally concerned with Babylonian notions of the war between Chaos and Order, and Nietzschean notions of power and responsibility. The titles of the entire series are themselves a philosophical statement, and they resonate with the target audience because they pull at, and subvert, ideas that anyone who reads SF or Fantasy is steeped in to the point they don't even realize it.
So these are titles with immediate resonance because they hook into something deep in the cultural consciousness, often without the customer knowing what they're doing.
But there is another kind of resonance--an acquired or secondary resonance, if you will. These are titles which require a bit of thought, but which become unforgettable after that initial bit of thought. For example:
The Unincorporated Man by Eyton and Dani Kollin. This is a double-take title if I've ever seen one. The mental process it elicits goes something like this: "The concept that a person is not a corporation is so basic as to be completely obvious, right? But if it's SO obvious...then why make it the title of a book?" If you make it that far in the trani of thought, they've got you. You're hooked. Even if you don't buy the book, you WILL remember the title.
The Pit and the Pendulum by Edgar Allan Poe. Yeah, we've all heard it so often that it feels like immediate resonance, but it's really not. It's a non-sequitur--he's putting together two things in this title that really don't seem to belong together, and yet they hint as desperate suspense. Pits, after all, are deep, dark, unpleasant places, and in Poe's time "The Pit" was the preferred polite term for "hell." Pendulums, on the other hand, regulate clocks, and signify order and dependability--so right away you have a very short mental journey from "a list of nouns" to "a terrifying juxtaposition," and that's enough to make the phrase stick in the mind, which makes it a great title.
The Long, Dark Tea-Time of the Soul by Douglas Adams. Adams was a master of titles that twisted the language just enough to mke them stick, and this one might be his best. It's a mash-up of that most British of civilized frivolity (tea-time, that pseudo-meal of tea and desserts and nibbles at 4pm) and one of the most potent metaphors for despair and depression in the English Language (The Dark Night of the Soul, from the poem of the same name by St. John of the Cross, 16th century). So, what do you get when you throw together civilized frivolity with existential angst? A title that makes you go "huh?" long enough to pick the book up and read the back.
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Now that we've seen how titles work, let me let you in on a few tricks I've seen other authors use (or used myself) in creating catchy titles:
Juxtaposition: setting two contradictory elements against each other in a way that suggests a deeper consilience, or which promises a gripping conflict, or both.
Cultural cannibalism: stolen quotes and aphorisms, sometimes (but not always) mangled just enough to pull them out of background cliche` and make them fresh. Examples include almost all of Agatha Christie's titles.
Subversion: As in the Douglas Adams example above, taking images from the cultural background and subverting them to suggest a mystery or explanation within the pages.
Movement: I once wrote and directed a film called The Hunting of Kestral Mannix, which sounded a lot grander than the film aimed at being. Eventually we retitled it to Hunting Kestral. The title change made raising money and casting the film MUCH easier, because the tense is active and the title suggests movement.
Atmosphere: Titles that deal primarily with weather or emotions can be effective and evocative, such as David Guterson's Snow Falling on Cedars.
Surprise: A title which is simply too ridiculous to be taken seriously, to the point where it can't pass unnoticed. Examples: Ice Pirates, The Unincorporated Man.
Allusion: A title alluding to another famous title can be quite effective. Agatha Christie's And Then There Were None has proved useful to me twice. In the first instance, it was originally released in the US as Ten Little Indians, also the title of a poem in the book which is structured like a slasher film (the book became the blueprint for slasher films, despite its genteel aesthetic). This led directly to the title of my own book Down From Ten, which has a few plot similarities (though only a few) and works on a countdown-clock structure, with each chapter title counting down from day ten to day zero. I'm told the title is arresting--if it is, it's because I cheated and borrowed a bit of Dame Agatha's thunder.
Of course, the same title also served as inspiration for my own book And Then She Was Gone. Same cadence, almost all the same words, but with a plot very different. The reason? It's a damn good cadence--it's very suggestive, it's a sentence fragment, it's evocative, and everyone has heard the old title, even if few have read the book, so it sets up immediate resonance: the title feels familiar in exactly the way I wanted it to. 80% familiar+20% alien=intriguing.
Pun or Double Entendre: Seth Harwood's Jack Wakes Up refers both to awakening from sleep (at the beginning of the book) and to awakening from a mid-life stupor. Ken Follet's Eye of the Needle is a complex pun: his villain is codenamed "The Needle", the story depends on his perspective, in the climactic sequence his eyes are injured, and he is the proverbial rich man (or, at least, well-financed by the Germans) attempting to get into the kingdom of heaven (or, receive the honors due him in his home country, to which he can't wait to return).
Recombination: Some authors keep interesting titles, and then combine bits of them at random. You can get some great stuff this way. For example, combine Stranger in a Strange Land with The Jaguar Hunter to get The Stranger in the Jaguar or Hunting the Stranger or any number of other permutations (notice that this is not my preferred way, as I'm not all that great at it).
And, of course, there's hundreds of other ways to do things: Euphemism, Dysphemism, Jargon, appealing to status, an interesting character name (Amadeus), a defining characteristic of an important character (The Time Traveller's Wife), or a totemic image (The Piano, Captain Correlli's Mandolin). You can go on forever with techniques for titles just as you can for techniques for storytelling, but the important factor remains the same, and it's still one word long:
Resonance. Shoot for that, and you may find titles just a little easier.