Before revision: In philosophy of language, a context in which a sub-sentential expression e appears is called extensional if and only if e can be replaced by an expression with the same extension and necessarily preserve truth-value .
After revision: In philosophy of language, an extensional context (or transparent context) is a syntactic environment in which a sub-sentential expression e appears is called extensional if and only if e can be replaced by an expression with the same extension and without affecting the truth-value .