“Is it Ladies Lunch or Ladies’ Lunch?”, asked an inquisitive mind on Grammar Girl’s Facebook page.
If you were writing a story in which the main character, a woman named Maude, goes out and paints the town red, would you call it “Maude Night Out”? Absolutely not. You’d call it “Maude’s Night Out”. The same rules apply for plural nouns. If the two characters happen to have the same name, it’s “Maudes’ Night Out” or “The Maudes’ Night Out”. The same would apply to a lunch for one lady or many ladies. If I ask the server where the lunch ordered by my wife is, he should reply “The lady’s lunch will be right out”, not “The lady lunch will be right out”. If I ask the server where the lunch ordered by my sisters (they are sharing a lunch today) is, he should reply “The ladies’ lunch will be right out” not “The ladies lunch will be right out”.
Though it is called, wildly inaccurately, the possessive case, possession has nothing to do with it most of the time.The ladies don’t own the “lunch”, nor is “lunch” an attribute of the ladies which could be reasonably paraphrased as being something they could possess or have in any possible way, not even at a stretch!. It is a lunch FOR the ladies. Nothing more. And that can be expressed by putting “ladies” into the genitive case and placing it in front of “lunch”: “ladies’ lunch”. The genitive case expresses a wide range of relationships between two nouns–about 40% of which are actual possession: my big nose, our shoes, Seth’s car. These are things that actually belong to someone. The other 60% are the non-possessive type: a dog’s owner, Ladies’ Lunch, the silent majesty of a winter’s morn, two weeks’ notice, March’s cruel weather, my greengrocer, my Morgan Stanley guy, my nosy neighbour, or my bid to become a world-class hot dog-eating champ.
Whether indicating actual possession or non-possession, a noun in the genitive case functions as a determiner, modifying the noun which follows it, a function which can be usually paraphrased as “determines which one(s) or which kind(s), based on certain relationships that exist between the two nouns”. In a case of actual possession, such as “Seth’s car”, “Seth’s” reduces the field of possible cars down to the car of which Seth is the legal owner. This is the typical case, but by far not the only case. Cruel weather occurring when? In March. How much notice? Two weeks. Which greengrocer? The one I buy carrots from. A morning occurring in which season? Winter. Which nosy neighbour? The one who lives next door to me. Who is trying to be a hot dog-eating champ? Me.
There is simply no need to invent elaborate secondary definitions of the word “possession” to describe relationships between two nouns which have nothing to do with possession or ownership. This error can be traced to Bishop Lowth. He’s grammar history’s greatest monster, if only because he has been so blindly followed by the equally well-meaning grammarians and teachers who followed his ill-conceived personal stylistic preferences.