A sentence is a closed formula, with no free variable occurrences. Its truth does not depend on a variable assignment. A first-order sentence uses a first-order formal language.
Articles by others on the same topic
In mathematical logic, a *sentence* is a well-formed formula (WFF) that does not contain any free variables; in other words, it is a statement that has a definite truth value—either true or false—once the variables are assigned values from a specific interpretation.