What's the technical, historical difference between an American diner and an old-fashioned coffee shop? How did coffee shops develop?
So I want to start by disclaiming that by coffee shop, I don't mean the places that have proliferated since the 1970s where a barista makes espresso behind a counter. I mean the old-school diner-like establishments that historically called themselves coffee shops or cafes. Here's an example.
So I know diners developed on the east coast, and for most of the 20th century the term diner referred to prefabricated dining cars like you see in New Jersey. At roughly the same time though, you get establishments that, like diners, have counter stools, booths, and serve coffee along with short order food like burgers and pancakes.
For most of the last century, most people on both coasts understood that coffee shops and diners were not the same thing. The structure of the building was seemingly the primary deciding factor. Even today, i have run into many folks who grew up on the east coast who insist that a coffee shop is not a diner.
The history of the diner is fairly well-established, but I can find almost no historical information on where coffee shops as we know them today came from. Why did coffee shops pop up in places like Chicago and Los Angeles starting in the 1920s (e.g. Lou Mitchell's, The Pantry)? Why did they take the physical form that they did? What would have made them different from other restaurants at the time? And at what point did people stop taking the difference between diners and coffee shops so seriously and start conflating the two?