The Baroque period covers roughly 150 years of music history, divided into the early (1605 to 1630), middle (1630 to 1680), and late (1680 to 1750) periods. Just a quick detour into music theory. Baroque music introduces the figured bass (also known as the thorough bass), as composers began what was to become an obsession with harmonic progressions that continue to this day and across all genres of music. The figured bass part was played by one or more instruments (often a harpsichord, possibly joined by a cello or viola da gamba), collectively referred to as the basso continuo. Here is a much more detailed explanation: http://openmusictheory.com/thoroughbassFigures.html.
The figured bass also gave rise to the practice of basso ostinato or ground bass, essentially a repeating pattern in the bass line. For example, listen to the first eight notes of the following—one of the most famous examples of ground bass in music history:
Johann Pachelbel, Canon in D: https://www.youtube.com/watch?v=JvNQLJ1_HQ0
Pachelbel creates the harmony from the ground up; hence, ground bass. This is no longer the fixed drone of Renaissance polyphony—harmony, beginning in the Baroque, is free to journey away from the home tonic chord, led by the bass line. Chords, rather than individual notes, could provide a sense of emotional closure—something noted by Monteverdi in his seconda practica. No longer just a piercing high C (think back to Allegri’s Miserere and its high notes), this is more the emotive satisfaction of riff based on power chords. The notable effect of this new method of composition was to confine melody in a single voice (as opposed to multiple voices in polyphony), supported by accompaniment, i.e., monody, paving the way for opera, concertos, and more popular musical forms. These basso continuo parts, and the concept of the basso ostinato, links Western music across the centuries, beginning in or around 1600 to the present, from Beethoven’s symphonies to Count Basie to some of the best-known rock tunes.
The Beatles, Day Tripper: https://www.youtube.com/watch?v=2IbPn5j2YKk
Led Zeppelin, Immigrant Song: https://www.youtube.com/watch?v=y8OtzJtp-EM
Baroque composers were now free to explore the relationships between the multiple melodic lines and the figured bass line, a compositional technique called “counterpoint”—literally point on point—which would come to dominate the Baroque Era. Here is a short video that provides an excellent introduction to contrapuntal technique: https://www.youtube.com/watch?v=4O6lc_ym12U. Although counterpoint was present prior to the seconda practica, Monteverdi’s embrace of dissonance led subsequent composers to explore a greater range of tone color in their music. Harmonies therefore became more complex as composers both identified the natural affinity between chords, as well as how multiple tones could combine into new chords.
The culmination of these explorations in counterpoint manifested in the fugue form. Technically, a fugue is a “contrapuntal compositional technique in two or more voices, built on a subject (theme) that is introduced at the beginning in imitation (repetition at different pitches) and recurs frequently in the course of the composition.” I think it is easiest to understand as the same basic melodic line (the subject) repeated at different times and at different pitches and meters, like Row, Row, Row Your Boat (in its most simplistic form). It opens with a short main melody (ending with “stream”), which is then repeated successively in each ensuing voice. When each voice has entered, the exposition is complete. Most fugues will then move on to more complex “development”, exploring different keys where material previously heard is transformed and transfigured, before returning to the home key for the recapitulation. Some fugues have a coda at the end.
Fugues are magical things. All you need is a simple tune to start and, frankly, it doesn’t need to be anything great. So, let’s pick a recent example from the top of the pop charts:
Ed Sheeran, Shape of You: https://www.youtube.com/watch?v=JGwWNGJdvx8
Not exactly great music. But give the tune over to a talented composer, unleash the contrapuntal power of the fugue and—BOOM:
Ed Sheeran (arr. Giovanni Dettori), Shape of You: https://www.classicfm.com/discover-music/ed-sheeran-fugue/ (see embedded link)
And if you want to hear a shorter vocal-only version:
Ed Sheeran (arr. Giovanni Dettori and Chris Rupp): https://www.youtube.com/watch?v=GZfHRZOFUGM