"Be based" is an often-used phrase in writing to indicate a foundation or underlying principle. However, there are several synonyms for this expression, including "stem from," "originate from," "grounded in," and "rooted in." "Stem from" implies that something is an outgrowth of another thing, while "originate from" indicates where something has its beginnings. "Grounded in" suggests that something is firmly rooted in a particular place or idea, while "rooted in" emphasizes the foundation or source of something. All of these synonyms for "be based" can add variety to your writing without changing the meaning or intent.