Why did Claudio Monteverdi use dissonance in his madrigals?

Claudio Monteverdi utilized dissonance in his madrigals primarily to ensure that his music precisely matched the mood and natural declamation of the lyric poetry he set to music.1

Influenced by the avant-garde movement of the 1590s, Monteverdi believed that the primary goal of his art was to "move the whole man." To achieve this, he prioritized the emotional expression of the verse, often at the expense of conventional musical balance. By employing intense and prolonged dissonance, he was able to capture every nuance of the text, creating a powerful, heightened emotional experience that traditional, purely polyphonic styles could not convey.1

While this approach provoked criticism from conservatives who favored older, stricter musical conventions, Monteverdi defended his methods as part of a tradition seeking a union of words and music. He viewed these dissonances as essential tools for dramatic unity and emotional impact, allowing him to reflect the tension, eroticism, or agony inherent in the poetry he chose.1