American journalist Jesse Kornbluth writes that, when AIDS first appeared in New York in the 1980s, Cantus was said to be the favorite music of men in the final weeks of their lives — "[f]or this music both acknowledges grief and suggests completion. It is, as Pärt has described it, 'like light going through a prism'."
It is scored for string orchestra and bells (only a single chime is used, on the pitch A, the tonal centre of the piece). Cantus is an example of Pärt's tintinnabuli style, using only the pitches of a single A-minor scale. This work is based on a very simple idea which is a descending A minor scale and is in the form of a prolation canon, an old technique which Pärt also uses in the work "Festina Lente" (or Hurry slowly). It is in 6/4 meter and alternates long and short notes.
Part has said of "tintinnabulation": "The complex and many-faceted only confuses me, and I must search for unity. What is it, this one thing, and how do I find my way to it? Traces of this perfect thing appear in many guises — and everything that is unimportant falls away. Tintinnabulation is like this. Here I am alone with silence. I have discovered that it is enough when a single note is beautifully played. This one note, or a silent beat, or a moment of silence, comforts me."
The whole piece is a meditation on the theme of death. Pärt's biographer suggests that "how we live depends on our relationship with death: how we make music depends on our relationship to silence."
It is significant that the piece begins and ends with silence, i.e. that the silence is written in the score. What this means is that although the various instruments appear to enter progressively, they are actually "playing" right from the start. This silence creates a frame around the piece and can be seen as having a religious or spiritual significance. It suggests that we come from silence, and return to silence, it reminds us that before we were born and after we die we are silent with respect to this world.
Each part except the viola is split into two, with one playing notes from the A Minor scale, and the other playing only notes from an A minor Chord (ie A C E). For Pärt this has a definite symbolism. The latter "always signifies the subjective world, the daily egoistic life of sin and suffering, [the former] meanwhile, is the objective realm of forgiveness." For Pärt, there is only an apparent dualism here; he believes that "all is one." Music is very good at demonstrating the combining disparate elements to make something greater than the sum of the parts — this music seems to exemplify the principle.
The A natural minor scale has some historical connections. Before the modern notion of scales music, especially the early liturgical music which has been so influential on Pärt, used a system of modes. These modes were known to the ancient Greeks and each was said to have a specific character which could strongly affect the mind, although we no longer know for sure which modes the Greeks were using. The church modes result from using the notes of the C major scale, ie the white keys on a piano, and starting at a different note. A minor is also known as the Aeolian mode. Since all minor scales derive from the white keys on the piano played from A to A, in choosing the A minor scale Pärt is acknowledging his debt to early church music, or at least affirming his affinity with it.
After three beats of silence a tubular bell is struck three times very quietly (pianissimo) with 12 beats between the strikes and gap of 18 beats between the groups of three. This bell tells of the death of Britten - it is the funeral bell. It continues to be struck in groups of three widely spaced intervals for most of the piece, fading out for a time in the last 21 bars, only to reappear at the last. After the bell has struck there is a brief pause for three beats of silence, and then the first violins begin setting the pattern which the rest of the ensemble will follow at slower speeds. Half of the first violins begin playing the descending A minor scale, playing first one note from the very top of their range, then returning to the beginning and playing two notes, and then three and four and so on. The other half of the violins play notes from an A minor chord. These notes start a fourth lower and drop in pitch only when it is over run by the first. This creates a swirling effect of increasing tension which is relieved by dropping the note. They begin playing very very quietly (pianissimissimo) but gradually over the piece build up until they are playing very very loudly (fortissimissimo).
The second violins play exactly the same but an octave lower and at half the speed, which means they play 6 beats (one bar) of silence to begin with, and appear to enter at the beginning of the second bar. Then the violas, which are the only voice which is not doubled, join in at a quarter speed and another octave lower, the cellos at one eighth, and finally the contra-basses as one sixteenth. The basses are then playing each note for 32 beats for a long note, and 16 for a short one which means that the piece requires enormous concentration.
After an initial phase which feels unstable and off center, perhaps even off key at times, the piece settles down and as the sequences of notes begin to grow longer the various rhythms and pulses become more evident. Cantus has a kaleidoscopic feel at times, but there once it becomes established there is a definite questing downwards, a searching, probing quality, a descent into darkness.
At bar 65 the first violins hit middle C and when they do they cease playing the A minor scale and simply play C continuously until the end of the piece (ie. for more than 250 beats). Eleven bars later the second violins hit a low A and play that continuously. Similarly the other voices gradually find the note that they have been seeking and once they get there they play it continuously until the end. The last to lock into place are the contra-basses which alight on a low A in bar 103. At this stage the whole ensemble is playing an A minor chord very very loudly, and this continues for five bars, then the second beat of the last bar they suddenly stop. At that moment the bell is struck very quietly (pianissimo) so that the striking itself is not heard, but only the reverberations as it dies away. As the final bell toll reverberates, with all other instruments silent, the overtones of the bell become prominently audible — in particular, the fourth overtone (fifth partial), which is the note C-sharp, i.e., the major third of the fundamental pitch (A) of the entire piece. This creates a striking effect, as the entire piece is set in the key of A minor, so that in the dying echoes of the final bell, the last thing the listener hears is actually an A major chord contained within the overtones of the bell. This evokes the common Renaissance and Baroque technique called the "Picardy third," in which a piece set in a minor mode or key nonetheless ends on a major chord, evoking a ray of light piercing through the clouds, and suggesting hope, resurrection, or redemption. Here, however, the effect is supremely subtle, because it arises solely from the overtones of a single strike of the bell, rather than from separate instruments or voices.