Salva Congruitate is used in logic to mean that two terms may be substituted for each other while preserving grammaticality in all contexts.
[3][4] Timothy C. Potts describes salva congruitate as a form of replacement in the context of meaning.
[6] Thus the singular term 'Bob' may be replaced by the definite description 'the first man to swim the English Channel' salva congruitate.
Such replacement may shift both meaning and reference, and so, if made in the context of a sentence, may cause a change in truth-value.
More generally, expressions of any type are interchangeable salva congruitate if and only if they can replace one another preserving grammaticality or well-formedness.