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]
(..) Excuse me, hello? My parents are trying to marry me off to a stranger. What am I going to do? - I suggest you go through with it. - What? Romantic love as the basis for marriage has only existed since the th century. Up until then, arranged marriages were the norm and it served society quite well. (..)2007 TvShow: The Big Bang Theory Title: The Grasshopper Experiment Season: 1 Episode 8