Third Species · Theory

Second Species Fourth Species Non-Chord Tone Treating Non-Chord Tones First Species

Third species splits each step further: one note of the cantus firmus against four notes in the counterpoint.

The texture changes from "one step at a time" to a run of notes — and within a run, dissonances may come in succession.

The unit of judgement moves from note to group

This is the crucial shift in third species:

	Second species	Third species
Unit checked	each note	the first note of each group
Where dissonance may sit	weak beats only	anywhere except the group head
How many	one	may come in runs

The ear counts the head of each group (it falls on a strong or secondary strong beat). The remaining three notes, provided they move by step, quickly, and without resting, will not be heard as arrival points even if they are dissonant in succession.

Three ways to handle dissonance inside a group

Type	Shape	Note
passing	stepwise filling	as in second species
neighbour	leaves and returns	a detour
the leap exception	entered by step, left by leap (then returning by step)	the only permitted leap treatment here, because the entry and exit are both defined

The third needs care: it applies only in that specific shape. Leaping into and out of a dissonance at will is wrong in every species (see treating non-chord tones).

It is closer to real writing

Second-species texture still feels like an exercise; third-species figuration (runs at one note value) is one of the commonest textures in real music — Bach's two-part inventions, fugal episodes and Classical accompaniment figures all belong to it.

So from this stage onward, judgement depends increasingly on whether the whole sounds like music, not on whether each cell is compliant. That is precisely the design of the species ladder: the looser the rules, the more musical judgement is required.

Diagram: the unit shifts from note to group

Listen: group head versus inside the group

Third species is a two-voice exercise and cannot be played here. Use interval to compare an interval usable at a group head with one usable only inside: a third (countable), then a second (a quick pass only).

Common misconceptions

"Dissonances may now go anywhere." Only their position is relaxed, into the group; their treatment

(by step, non-resting) is unchanged.

"A group of four must be all the same note value." In the exercise, usually; in real writing it varies, at

which point you are in fifth-species territory.

"Third species is much harder than second." Only one rule is added (the head must be consonant); the real

difficulty is that the point of judgement moves from note to group.

"Figuration is only an accompaniment device." It is also a fundamental polyphonic texture — Bach's

inventions and fugal episodes use it heavily. :::

Listen in the library

Invention 08C11:06Bach's eighth two-part invention — runs of four notes contain strings of dissonance, exactly third-species textureDetailsInvention 1C11:03Bach's first two-part invention — its figurated passages are denser, showing the difference from second speciesDetailsScales, Arpeggios, and CadencesC13:22Scale exercises are literally groups of four stepwise notes, useful for spotting which note is heard as the frameDetails

All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).

Sources

第三类对位（四音对一音）规则：每组第一音须协和、组内可用不协和音且须级进处理，为通行对位教学体系
一组之内不协和音的处理方式（经过、邻音、以及跳进的例外）为对位学通则

Used for fact-checking only; all prose is original.

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