Nowadays, of course, it's pop culture, not the literary canon, that's the main source of this. Whether it represents decadence and rampant philistinism or a more accessible, egalitarian spirit is up for debate. Some traditionalists might have taken hope from Dead Poets Society (1989) giving new life to Horace's "Carpe diem", but it didn't lead to a massive mining of the ancients.

Movies, of course, provide many examples of this common referencing - in memes, quotes, headlines, allusions, riffs, and more. It's assumed audiences and readers will be sufficiently familiar with particular lines - and variations thereon - to understand and appreciate the humour, piquancy or other intended effect. Some movie quotes only have their effect in context - calling to mind the appeal of a particular scene or film - but others can transcend their origins to become widely used.

Frankly my dear, I don't give a damn. Follow the money. Fasten your seatbelts, it's going to be a bumpy night. You can't handle the truth. All right, Mr DeMille, I'm ready for my close-up. I coulda been a contender. Hasta la vista, baby. Nobody puts Baby in a corner. I feel the need - the need for speed. That's not a knife: that's a knife. This is going straight to the pool room.

How many of these do you recognise, from their original contexts and from the ways and places they've been used since? I'm betting it's most, if not all of them. You've seen the movies - they include Gone With the Wind, All the President's Men, On the Waterfront, All About Eve, Top Gun, Dirty Dancing, The Castle, Crocodile Dundee, and The Terminator - and you've read them in headlines, heard them on TV shows, even used them yourself in conversation. And if you're a Monty Python fan, chances are you've committed most of Life of Brian (and much else) to memory.

The eminently quotable Casablanca comes in handy. While it's well known that "Play it again, Sam" is a misquote - Ingrid Bergman says, "Play it, Sam" and Humphrey Bogart says, "Play it"- there's plenty of other material. The film's dialogue ranges from the romantic ("Here's looking at you, kid"; "We'll always have Paris") to the cynical. People will claim disingenuously they are "shocked, shocked" and promise they will "Round up the usual suspects".

Some movie quotes take a while to pass into the vernacular. Scarface wasn't terribly well received when it premiered in 1983, but increased in popularity over the years. Al Pacino's intense, pseudo-Cuban accented rendition of the line, "Say hello to my little friend" - said friend being a machine gun - led to it latterly becoming something of a standard. Perhaps its early fans aged into animators: it turned up in more than one recent animated movie, a little wink to the adults in the audience.

Other movie quotes are taken up almost immediately. Think of Liam Neeson's speech to the kidnapper in Taken - including his declaration that he has "a very particular set of skills" and promising that if his daughter is not released, " I will look for you, I will find you, and I will kill you".

In their blunt toughness, Neeson's words are reminiscent of a couple of Clint Eastwood's taunts: "You've got to ask yourself one question: 'Do I feel lucky?' Well, do you, punk?" (from Dirty Harry in 1971) and, from Sudden Impact (1983), "Go ahead, Make my day". The latter was taken up by US president Ronald Reagan in 1985: "And I have only one thing to say to the tax increasers. Go ahead - make my day."

The Wizard of Oz (1939) is loaded with indelible lines quoted to this day: "Toto, I've a feeling we're not in Kansas any more", "Pay no attention to that man behind the curtain", "I'll get you my pretty, and your little dog too".

Some lines are little more than catchphrases - Austin Powers' "Yeah, baby!", Wayne and Garth's "Not!", Bill and Ted's "Excellent!" - but they still hit the sweet spot of memorability at just the right time with just the right audience and endure.

Of course, some great movies aren't very quotable, and quotability doesn't necessarily mean a movie is great. The Room has dialogue memorable both for its badness and for the bizarre quality of its delivery. Tommy Wiseau referencing James Dean in Rebel Without a Cause makes the notion of being emotionally torn apart hilarious rather than poignant. And Plan 9 From Outer Space has lots of lines that seem so sincere in their goofiness they are fun, right from the welcome by the narrator: "Greetings, my friend. We are all interested in the future, for that is where you and I are going to spend the rest of our lives."

There are lines, too, that only really work if you know the movie in question. "Well, nobody's perfect" sounds plain but ends Some Like It Hot perfectly, and cultists will quote lines like "On Wednesdays, we wear pink" (Mean Girls) as in-jokes for the initiated.

Which lines will become indelible, part of the common parlance? It's impossible to predict - which is part of the magic of the movies.