|Tagliatelle al Ragù (Bolognese)|
"Sugo" or sauce is a general term that indicates a fluid sauce. It can be a simple tomato sauce like a marinara or can include whole plum tomatoes and some other ingredients, cut small.
A ragu' is a thick, chunky sauce usually made by cooking several kinds of meat in a sauce, usually tomato. That said, a ragu' can also made with seafood, vegetables or a combination of these.
The most famous ragu's in Italy are the Bolognese and the Napoletan but almost every region (and sometimes cities) have their own ragu'. In fact, its not necessary to specify which ragu' you are preparing or talking about unless you are talking about a ragu' from a different town!
A Bolognese ragu' is made with ground meat cooked with vegetables and a small amount of concentrated tomato, added for color. The Bolognese ragu' is served with tagliatelle pasta. The Napoletan ragu' has lots of onions and a big chuck of beef that cooks in the tomatoes for many hours. You are supposed to serve the beef flavored sauce with spaghetti or linguine pasta and serve the meat as a second course. Still the "sauce" is considered a ragu'. The Pugliese ragu' includes several types of meats including ribs, porkchops and beef. The "sauce" is served with orecchiette pasta while the meats are served as a second course. And again, the "sauce" is considered a ragu'.
Its interesting to note that East coast American-Italians call their meat sauce "gravy" instead of sauce. Its clear that the old timers who emigrated to the US wanted to differentiate the fluid, tomato sauce from the meat sauce; just like the relatives back home distinguish "sugo" from "ragu".