The affectation of key in Dido and Aeneas is used explicitly to evoke different moods throughout the opera. Purcell uses major keys to evoke moods of happiness and minor keys to evoke sadness, as do most other composers so this shows that Purcell has followed the normal structure of an opera.
The first scene of the opera, where Dido is unhappy and afraid of falling in love with Aeneas who has a destiny to fulfill, is in C minor. This key is most often associated with tragedy or anguish because of its sad and mournful sound. This is part one where part 2 (where Aeneas first enters the palace) is in C major, the opposite and overall more optimistic sounding tone gives the listener a feeling of encouragement (even Belinda is optimistic that Dido’s emotions can excel over Aeneas’ fate).
The next scene (where the plot of the opera unfolds) is the cave scene where the witches devise their plan to separate Dido and Aeneas, since the key shifts from F minor to F major, it is clear that we as the listener are meant to be horrified by this planning of evil (F minor is the lowest note on the treble, indicating a strong sense of horror and imbalance, where F major (in Purcell’s works) is the key associated with love. The two keys balance perfectly).
Although the overall key structure of the opera is balanced and neat, there are occasional interruptions that are worth noting, such as the D key of the grove scene interrupting the F tonality of the cave scene, and the E minor key of Aeneas’ entrance interrupting the C major key of the introduction of Dido. These keys all reflect different moods ranging from the feeling of hate to the power of the feeling of love; such is the organization of Purcell.
When looking at the placement of each key in the opera, it can be said that the opera can be divided into 2 large sections each containing three minor sections, these sections are occasionally divided by an act/ scene change or a change in destination (the cave scene transition to the grove scene for example, one minor section to another) each having its own tonal center as explained before. The one scene that has not yet been analyzed is the sailor scene, which is in the key of Bb; this is also the scene where Aeneas prepares to depart and leaves Dido to her anguish. The end scene (Dido’s demise) is in the key of G minor and thus concludes the opera; this key is generally associated with either royalty (G major) or death (G minor).
As said before, the overall key structure of Dido and Aeneas is surprisingly neat, using the technique of calculated tonal shifts gives the listener the feeling that the story is moving in different directions all the time, the key also tells the listener which mood they should be feeling at the time (since the opera is supposed to be performed as a play and not just as a listening piece). Although the play is supposedly incomplete (the argument of the tonal imbalance at the end of the grove scene) the key and story is not heavily impacted. It can be said that this is one of Henry Purcell’s greater works because of how much attention has been paid to making the key structure balance so well.