"So long as" is a phrase that means as long as or provided that. It can be used to express a condition or a requirement for something to happen or be true. There are several synonyms that can be used interchangeably with "so long as", including "as long as", "as far as", "provided that", "if", "on condition that", "in the event that", "assuming that", and "given that". Each of these synonyms carries a slightly different connotation or emphasis, but all indicate a condition or requirement that must be met for something to occur or be true.