When it comes to passionate love stories, there are two laws or conditions that make them seem especially memorable or magnetic. One, the best love stories are those which don’t end happily. (The late Sydney Pollack pointed this out time and again.) And two, love stories seem more passionate if the lovers never get around to actually doing it.

I’m not about to invest hours of research, but I’ll guess that a majority of anyone’s favorite love stories, from Wuthering Heights to Brief Encounter to Once, have been unconsummated. I would further guess that a list of popular love affair movies that have included actual sex would probably be fairly short.

I dove into this because it hit me this afternoon that one of the craziest and most erotically charged on-screen love affairs, the one between James Stewart‘s Scotty Ferguson and Kim Novak‘s Judy Barton (a.k.a. Madeleine Elster) in Alfred Hitchcock‘s Vertigo, never included the nasty. They made out under the Muir redwoods and along the Pacific coast and yes, Scotty did undress Judy/Madelyn after she passed out following a drowning attempt, but they never got down.

Who else abstained? Trevor Howard and Celia Johnson, of course in Brief Encounter, as well as Robert De Niro and Meryl Streep in that 1984 remake, Falling In Love. Robert Mitchum and Deborah Kerr in Heaven Knows, Mr. Allison (’57). Bill Murray and Scarlet Johansson in Lost in Translation. Humphrey Bogart‘s Phillip Marlowe and Lauren Bacall‘s Vivian Rutledge in The Big Sleep. Burt Lancaster and Katharine Hepburn in The Rainmaker (’56). Robert Forster and Pam Grier in Jackie Brown. Michael Caine and Julie Waters in Educating Rita.

Others? Does it matter? I could go on and on.