Canon Types and Techniques: Rounds to Crab Canons

One melody becomes many when voices chase each other through it. Canon is the strictest form of imitation: the follower reproduces the leader exactly, offset in time and pitch, and the composer must craft a line that sounds right both alone and against its own echo.

#Rounds and simple canons

A round is a canon at the unison with a catchy, triadic melody. Frère Jacques, Row Row Row Your Boat, and countless folk rounds share the same construction: short phrases that imply plain harmonies, so that staggered entries stack into consonant chords.

The opening of Frère Jacques above shows the requirements. Each two-bar unit outlines the tonic triad, the rhythm is foursquare, and no chromatic tones complicate the overlap. When the second voice enters two bars late, its C sounds against the leader’s E: a stable third.

Simple canons generalize the round to other intervals. A canon at the fifth has the follower reproduce the melody a fifth higher or lower; a canon at the octave doubles at the octave. The interval distance changes which harmonies the overlap produces, so the melody must be designed for its specific destination. A tune that works at the unison often fails at the fifth, where the implied roots shift.

The background craft is first-species counterpoint: note against note, consonant, with careful handling of perfect intervals. Every canon reduces to species intervals at each entry point, and the species rules predict which overlaps will sound clean.

#Time and interval distance

Two numbers specify any canon. The time distance counts the delay in beats or measures before the follower enters. The interval distance names the pitch offset: unison, second, third, up to the octave and beyond.

Short time distances create tight chases where the follower nips at the leader’s heels. Pachelbel’s Canon uses a two-bar delay over a ground bass, close enough that the violins feel conversational. Long delays let each voice establish itself; Renaissance Mass movements sometimes wait four or more bars between entries, and the texture breathes accordingly.

Interval choice shapes the harmony. Canons at the fifth and fourth suit dominant-tonic rhetoric, since the follower naturally answers in the neighboring key area. Canons at the third and sixth produce sweeter, more parallel textures. Canons at the second and seventh are deliberately pungent, generating suspensions and dissonances the composer must resolve on schedule.

Hear the same fragment at two distances. First at the octave with a one-bar delay feel, then the follower alone showing the fifth transposition.

The second line transposes the first down a fifth, preserving every interval. Whether the combination works depends on the vertical result at each offset moment, which the composer checks entry by entry.

#Strict, free, and fading canons

A strict canon maintains exact imitation to the end. Most rounds are strict; so are the canonic studies of Bach, Handel, and the serialists. Strictness is the default assumption when a score says canon without qualification.

Free canons relax the imitation after establishing it. Voices begin in canon, then diverge into independent lines or cadential formulas. Many fugal expositions work this way: the answer starts as a tonal imitation of the subject, then breaks free to serve the developing texture. The subject and answer relationship in fugue is canon technique bent to dramatic ends.

Fading or partial canons dissolve deliberately. The follower drops out, the leader varies beyond recognition, or new voices enter non-canonically until the chase texture dissolves. Haydn and Mozart use canonic openings that melt into homophony, borrowing the learned flavor without the learned obligation.

Accompanied canons add free parts beneath or around the canonic voices. The Goldberg Variations include nine canons at increasing intervals, each with a free bass line that supplies harmonic grounding the two canonic voices omit. The accompaniment frees the canon from having to be self-sufficient.

#Mirror forms: inversion, retrograde, augmentation

Learned canons transform the follower instead of copying it literally. The transformations combine freely, and puzzle canons notate only one line plus cryptic instructions for deriving the rest.

Canon by inversion. The follower mirrors the leader’s intervals: ascending steps become descending steps around a stated axis. The result sounds related yet contrary, and the composer must verify consonances that the mirror keeps rearranging.

Crab canon (cancrizans). The follower plays the leader backward. A melody that harmonizes with its retrograde must be palindromic in its harmonic rhythm, which severely limits its shape. Bach’s Musical Offering crab canon is the famous proof that the feat is possible and musical.

Canon by augmentation and diminution. The follower moves in longer or shorter note values, stretching or compressing the line. Mensuration canons from the Renaissance run three or more voices at different speeds simultaneously, and the proportions (2:1, 3:2) become part of the design.

Spiral canons. Each repetition modulates, so the canon climbs by key with every cycle. Byrd and Bach wrote spirals that return to the starting key only after exhausting a chain of dominants. The technique turns the canon into a modulatory machine.

These devices belong to the broader art of imitation and invertible counterpoint, where voices swap registers and roles without breaking the harmony.

#Where canons mislead people

The commonest failure is a melody that cannot harmonize with itself. Beginners write an attractive tune, offset a copy, and discover clashing sevenths and exposed tritones at every entry. The fix is to compose with the overlap audible from the first sketch: write two bars, enter the follower, check the vertical intervals, then continue. Canon melodies are written in pairs or not at all.

Cadences cause the second problem. Strict imitation gives each voice the same ending, so all voices want to cadence on the same beat with the same formula. Solutions include staggered cadences (voices arrive one by one), a coda after the canon dissolves, or a final entry that breaks strictness to supply the close. Plan the ending before writing the middle.

Singers add a practical constraint: canons must sit in comfortable ranges for every voice at its transposition. A round that fits altos at the unison may strain them at the fifth. Check the follower’s tessitura as carefully as its counterpoint, or the performance will punish the singers for the composer’s arithmetic.

#What to do with it

Write a four-bar melody in C major using only chord tones of I and V plus passing steps. Enter a second voice at the unison two bars late and check every vertical interval. Adjust the melody until the overlap is clean, then add lyrics or a neutral syllable and sing it with a friend. The singing test is merciless and final.

Next, transpose the follower to the fifth and repair the resulting clashes by adjusting the melody. Some measures will need new notes; a few may need rhythmic changes. The repair process teaches more about canonic constraint than any treatise, because each fix responds to a specific vertical failure.

Finish by studying one Goldberg canon with the score, marking the time and interval distances and the free bass notes. Then write an eight-bar accompanied canon of your own at the interval you find hardest. The accompaniment supplies the harmonic safety net while the two canonic voices practice the chase.

Questions

What is the difference between a canon and a round?

A round is a canon at the unison where each voice sings the same melody from the start, like Row Row Row Your Boat. Canon is the general technique: voices enter at stated time and pitch distances, which may be any interval and may transform the melody.

What do time distance and interval distance mean in a canon?

Time distance is the delay before the following voice enters, measured in beats or bars. Interval distance is the pitch offset between leader and follower, such as a canon at the fifth or at the octave. Both distances define the canon type.

What is a crab canon?

A crab canon pairs a melody with its own retrograde, so one voice plays the line forward while the other plays it backward. Bach's Musical Offering contains one. Writing a line that harmonizes with its mirror image is the contrapuntal challenge.

Can any melody become a canon?

No. A canon melody must harmonize with a delayed copy of itself, which constrains its intervals and implied harmony. Strong canonic melodies outline clear triads and move mostly by step, giving the delayed entry consonant support.