Did silent film actors actually say their lines or did they simply improvise “dialogue” while being filmed?

Question

Been watching some old Buster Keaton films. And—as is the case with silent films—there are title cards that convey setting, place and even show a few lines of dialogue that have been said by the characters on the screen.

But often it seems like actors are saying more lines than the title cards seem to convey that they are saying.

So did the actors in silent films improvise lines on camera, or was a script drafted that gave them lines to say so things seemed realistic and coherent when scenes were filmed?

Answer 1

It seems they did use scripted dialogue.

From the article Silent Movie Revisited with an emphasis of mine,

Third, one should also stress the important contribution of this book to the critical reappraisal of many stereotypes concerning the early years of the cinema, such as the (completely false) idea that silent movies were not scripted or that the actors did not really pronounce their lines as they were supposed to do. There is now a whole lot of evidence that those scripts existed, and that they really were the base of the whole production. Moreover, lip reading experiments have shown that the scripted lines corresponded with what the actors actually pronounced, and there are testimonies that the first spectators noticed when a "silent" actor pronounced, say, "What do we have for dinner tonight" instead of "I really love you, you know".

Of course, they said more lines than what written on title cards, but it is just to give the gist about what characters in the scene are up to.