In our contrapuntal studies, most of our encounters with canons are in isolation: pieces that are purely canonic such as every 3rd variation of the Goldberg Variations. However, not much justice is done to canons that appear as parts of a larger form and are more flexible in their treatment. That is, what I call canons in the wild. The reach of the canonic process in the repertoire (or wild) cannot be overstated, yet I find it is seldom observed (not to mention, seldom taught to students). From Bach to Bartok and Mendelssohn to Michael Jackson, the canonic process can be observed acting as a significant compositional process in their works.
One of the great Baroque masterpieces, Bach's Mass in B minor, was intended as a catalogue for a number of various styles and techniques - it is a true forest of music. Just as a biologist may learn secrets of life from a flower in the amazon, so too can a composer learn secrets of music from examining an aria from the Mass. Of course, as with most of Bach's works, the canonic process is employed heavily throughout the work. My personal favorite is Domine Deus, which features a dazzling display of the canonic process. But, I have opted for the equally refined and exquisite Et in unum Dominum for this discussion. So, let's wade into the sonic thicket of Bach's masterpiece...
Symbolum Nicaenum
Et in unum Dominum is part of the Symbolum Nicaenum (Nicean Creed), the second of four sections of the Ordinarium Missae (Mass Ordinary). It is a profession of faith that was carried out in the city of Nicea. For our purposes, we will dispense with the bulk of the text and focus on what Bach set in this specific aria:
Et in unum Dominum, Jesum Christum, Filium Dei unigenitum et ex Patre natum ante omnia saecula. Deum de Deo, lumen de lumine, Deum verum do Deo vero, genitum, non factum, consubstantialem Patri, per quem omnia facta sunt. Qui propter nos homines et propter nostram salutem descendit de coelis.
And in one Lord Jesus Christ, the only-begotten Son of God, begotten of his Father before all worlds. God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father, by whom all things were made. Who for us men and for our salvation came down from heaven.
Our analysis will focus on the soloists who begin the duet at the conclusion of the ritornello. The duet between soprano and alto enters on a restatement of the opening theme in a close canon at the unison over the words Et in unum - and in one. This is seamlessly transitioned into a canon at the 4th down over the Monte Romanesca on in unum Dominum Jesum Christum, Filium Dei unigenitum - in one lord Jesus Christ, the only beoggten Son of God. The canon breaks to carry the phrase to its cadence on et ex Patre natum ante omnia saecula - begotten of his Father before all worlds - and modulate to the dominant.
Here we learn how Bach employs the canonic process in a meaningful way to deliver the text. The text is divided into three parts: Et in unum | Dominum Jesum Christum, Filium Dei unigenitum | et ex Patre natum ante omnia seacula. That is: And in one | Lord Jesus Christ the only-begotten Son of God | begotten of his Father before all worlds. Notice that there is a crescendo to the language here as it moves through the 3 parts. The 8 bar phrase compliments this linguistic crescendo harmonically with a short tonic expansion under Et in unum, then a sequential Monte Romanesca under Dominum... unigenitum, and finally the cadential module (colloquially known as turn around, this term "cadential module" is borrowed from Caplin) in the dominant that delivers the conclusion of the phrase on et ex Patre...saecula. Achieving the dominant on Patre - father - is worth noting, since the triad was often used as representation of the Holy Trinity. The root for Holy Spirit, the mediant for the Son, the 5th for the Father. But an extensive discussion of this is outside of the scope of this article.
See how the canon unfolds from the unison to the 4th down from Et in unum to Dominum... unigenitum and breaks at patre saecula. The canon compliments the curve of the language and forcefully delivers the crux of the phrase when it cracks open to free counterpoint at the cadential module.
Moving on, we have the restatement of Filium Dei unigenitum - only-begotten Son of God - which is set to a canon at the 3rd below. This is elided with another canon at the 3rd below that returns on et ex Patre natum ante omnia saecula. Textual repetition in liturgical music is a common device that reinforces what is often the imperative mood of most religious texts (keep in mind that this particular situation is not in the imperative mood). We see this in services across the spectrum - from the docile to the most disturbingly fervent - repetition of religious texts is a powerful way to drive home how strongly you believe in something. The canon then breaks at the cadential module with the restatement of ante omnia saecula.
This canon is not too different from the previous one in how it starts with an initial imitation that is elided into an 8 bar canon at the 3rd down. It then breaks to deliver the cadence at the end of the phrase on ante omnia saecula. What is particularly interesting about this canon is the orchestral accompaniment. Notice that during the initial imitation between the voices, the strings also form a canon at the 3rd, creating a brief duplex. When the voices embark on their second canon, the strings then imitate each other in contrary motion (though they do not constitute a proper canon).
With those observations, you are equipped to examine the rest of the aria. There are a number of other canons like the ones pointed to in this article. Rather than hold your hand, I think you'd be better off exploring this subject on your own - this will make for a lesson well learned! There are deep lessons in Bach's music on how the selection of the type of canon can deliver the the linguistic and musical phrase. Here are some other works that feature canons in the wild. I encourage you to seek out the translations of these texts and see how the canon accompanies the language and delivers the phrase.
Christe Eleison, Mass in B Minor, BWV 232
Domine Deus, Mass in B Minor, BWV 232
Von Den Stricken Meiner Sünden, St John Passion, BWV 245
So ist mein Jesus nun gefangen, St Matthew Passion, BWV 244
Ach, wenn wird die Zeit erscheinen, Christmas Oratorio V, BWV 248
Suscepit Israel, Magnificat, BWV 243
Erfreut euch, ihr Herzen, BWV 66
There are many more canons you can find in the vocal and instrumental works of Bach alone. Of course, he is the exemplar of canonic technique, but don't forget about Vivaldi, Händel, Mozart, Beethoven, Mendelssohn and even Bartok! There are plenty of canons to be discovered in the wild.
If you're interested in not only studying but also mastering and applying these concepts, consider reaching out to me for lessons!