In the first half of the 20th century, the majority of movies were not rated. Heck, they were not rated, they were certified if you want to get technical.

The majority were simply certified. Such movies under today's system would be rated G or a very mild PG.

Now for the big one. Ever wondered where the mythical "X" rating came from?

In those days, a certification of X simply meant the movie went BEYOND that. The movie could have a rating ranging from the upper half of PG all the way up to NC-17 and/or a full blown porno.

An example of a good, clean, and non-pornographic movie getting a certification of X would be Midnight Cowboy. It was a movie about a hard on his luck homeless guy in New York City from what I hear.