So, here's Sourcery:

And here's Pyramids:

Interestingly different, yet fundamentally similar sentences.

Sourcery's first sentence is bold in its simplicity. Not even stopping for a 'once upon a time', it goes straight into a direct, monosyllabic statement: 'There was a man.' We hear nothing of his name, place, character or life: his mere existence is the substance of a story. This is fairy-tale logic - especially when the sentence adds the number of sons - but fairy-tale stripped of its traditional 'once upon a time' flourish. Pared-down fairy-tale, in other words; down-to-earth fairy-tale; fairy-tale stripped down to common humanity. Pratchett often makes a theme of the ordinary man (and, less often, the ordinary woman), and this stylistic bluntness prepares the way: we are to see the mundane humanity in the context of the mythical.

There is no such bluntness in the opening of Pyramids. In terms of style, Pratchett is more or less showing off here with his bathetic bump from the epic drama of 'nothing but stars' to the sudden hop from the divine to the ridiculous - or at least to the quotidian. In positing a Creator with a windscreen, Pratchett asserts his characteristic style in which he helps himself to analogies that would be foreign to his characters, while also cocking a snook at reverence: a Creator who can't be bothered is a clear declaration that we are in a comic universe. The sentence is elaborately, almost heavy-handedly comedic, the kind of sentence a publisher very much hopes will grab the attention of a casual bookshop browser; it's also a sentence that quickly lays out the stall. We are reading a book aimed at a modern reader that will touch upon metaphysics with a gadfly lightness.

What can we see in common with these sentences? Well, one of the major commonalities is that they turn and look the reader in the eye. 'There was a man' is the writer informing rather than evoking; windscreens and Creators assure us that we'll be looking at the universe through, as it were, our own, human-eye-level windscreen. In both cases, the overriding tone is conspiratorial.

At the same time, their scope is broad: the audience may be our ordinary selves, and the universe may centre on equally ordinary people, but myths and divinity are not beyond our reach. In fact, far from being beyond our reach, they are being brought down to our level. We can accept that the existence of a mythical man is important without needing a 'Once upon a time' to ease us into it; we can laugh at a wild night sky with a careless Creator. Pratchett at once appeals to and flatters his audience's intelligence. The universe is a joke, and we will be in on it.

Terry Pratchett is an author who begins with bold sweeps, often starting in the heavens or ranging over a whole city or country before narrowing in on his central characters. Beginning with a sentence that grabs the readers' attention with its eccentricity is often a successful strategy, commercially as much as artistically (Iain Banks is a notable example), and a common feature is that the style tends to settle down once the story begins. There is a limit to how much you can tell readers about the actual events of the plot when you're in the realm of the mythic - or at least, there's a limit if you're going to make your story about ordinary people and tell it in a chatty, colloquial tone as Pratchett does.

As a result, Pratchett's opening sentences are often, in terms of storytelling, skippable. While they vary in content, they tend to have a single declaration: You are reading a Terry Pratchett novel. Humour, irreverence, metaphysics and myth are going to be featured, and we'll get to the plot in a minute. I said in my discussion of Jane Eyre that some books begin with a handshake, and Pratchett takes this a step further: in effect, his first sentences are secret handshakes. Open secrets, secrets that the reader can work out by getting the joke - as I said, one of Pratchett's main charms is that he makes the reader feel clever - but coded handshakes nonetheless. You shake the sentence's hand, and then you get admitted into the clubhouse.

I would note an interesting fact here: Pratchett is a writer who tends to elicit strong positive or negative reactions, and the negative reactors often plough down in the first few pages. The first couple of times I tried his books, this is how I reacted; I found the beginnings repetitive and mannered, and it was only when I persevered into the plot that I started enjoying it - and subsequently developed some appreciation of his openings. Other readers, I think, delight in the sense of 'Welcome back!' that his sentences create, the way they invite a sense of membership. Pratchett is an author unusually able to establish a sense of friendship with his readers - not necessarily in terms of how he behaves in person (though I get the impression he's a pretty friendly chap), but by establishing a style and inviting his readers in.