The phrase "if not" is often used to express a hypothetical scenario or an alternative possibility. It can also serve as a connector between two clauses in a sentence. However, there are several other phrases that can be used interchangeably with "if not" to provide greater variety in language. Some examples include "unless," "except for," "otherwise," "in the absence of," and "but for." Each of these phrases conveys the idea of a conditional or alternative situation, and can be used to add nuance to a sentence or to improve its readability. By adding more synonyms for "if not" to our vocabulary, we can create more varied and expressive language.