The actor's letters form the 'basis' of the biography. [=the biography is based on the actor's letters; the most important information in the biography comes from the actor's letters]
This principle forms the 'basis' [='base', 'foundation'] of the country's economic policies and will provide a firm 'basis' for future development.
These stories have very little 'basis' [='foundation'] in fact/reality. [=these stories are not based on or supported by facts/reality]
(..) I'm afraid that you want to. You can't short the stock because Bruce Wayne goes to a party. Wayne coming back is change. Change is either good or bad. I vote bad. - On what basis? - I flipped a coin. Rye. It says rye. I said no rye, man. Hey, rookie! Lose the helmet. We need faces for camera. (..)2012 The Dark Knight Rises