Why are logically true sentences true in every interpretation?

In the philosophy of logic, a sentence is considered logically true if it is true in virtue of the meanings of the terms it contains, independently of any contingent matters of fact.1

Logically true sentences are true in every interpretation because they rely on logical constants—such as connectives like "and" or "if-then" and quantifiers—rather than on specific empirical content. When all nonlogical terms in a sentence are replaced by variables, the resulting formula exhibits its logical form. If this formula remains true under every possible substitution of interpreted terms, the sentence is logically true.1

Essentially, these truths are guaranteed by the structure of the language and the definitions of its logical operators, rather than by the state of the world. As noted by Bernhard Bolzano, a sentence is analytically true if its propositional form holds for all values of its variables. This ensures that the truth of the statement is preserved across any interpretation of the formal language.123