Sobre la fórmula fraseológica ¡mal pecado! en el Libro de Buen Amor

The main aim of this article is to offer an analysis of the idiomatic expression ¡mal pecado!, together with its variant por mal pecado, in its narrative context, in its diachronic evolution through its continuity in the texts of our literary history, as well as in its phraseological standardization in the framework of the history of Spanish Lexicography. The results obtained indicate that the formula ¡mal pecado! constituted a very profitable stylistic procedure when it came to bringing out the emotional component in the plot of the work.