In fourth species, the counterpoint melody and cantus firmus both move at a pace of once per bar, in a 1:1 rhythmic ratio as in first species; however, in fourth species, the counterpoint and cantus are rhythmically displaced from each other by the duration of one half note: they are syncopated. The counterpoint melody will be notated in half notes, with each weak-beat half note tied across the bar line to the following strong beat, while the cantus firmus will be set as usual on whole notes on each downbeat. This special arrangement means that in pure fourth species counterpoint, the two lines always move in oblique motion. This also introduces a new kind of possibility regarding dissonance: the suspension. This broad concept, handling the preparation and resolution of a dissonance by means of a suspension will appear in our later study of harmony.

Example 1 provides the complete examples of fourth species counterpoint from Part I of Gradus ad Parnassum, annotated (as before) with the interval that the counterpoint line makes with the cantus firmus.

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Example 1. All fourth species exercises from Gradus ad Parnassum.

The Suspension

The suspension is an accented dissonance, meaning it always occurs on strong beats. Because of the increased emphasis, even greater care must be taken to promote smoothness and overall coherence. Thus, like the passing-tone and neighbor-tone dissonances, the suspension is always preceded and followed by harmonic consonances. A suspension figure has three parts:

• Preparation: a weak-beat in the counterpoint that forms a harmonic consonance between the counterpoint melody and the cantus firmus. This note will be tied to the suspension, and thus are the same pitch.
• Suspension: a strong-beat in the counterpoint, with a note tied from the preparation, that forms a harmonic dissonance between the counterpoint melody and the cantus firmus.
• Resolution: a weak-beat in the counterpoint that has the suspension moving by stepwise motion downward, forming a harmonic consonance between the counterpoint melody and the cantus firmus.

Use dissonant suspensions as much as possible in fourth species counterpoint. The primary purpose of the exercise is to develop fluency and practice in the handling of the dissonant suspension.

Types of suspensions

Suspensions are categorized according to the harmonic intervals of the both the suspension and resolution tones formed with the counterpoint melody either above or below the cantus firmus (Example 2). A 7–6 suspension, for example, includes a strong-beat suspension that forms a seventh with the cantus, which resolves downward by stepwise motion to a weak-beat tone that forms a sixth with the cantus.

• Possible dissonant suspensions above the cantus firmus are 7–6, 4–3, and 9–8 (also 2–1). These are the only options that start on a dissonance and resolve down by step to an allowable consonance. 7–6 and 4–3 are preferable due to the resolution of the harmonic dissonance into harmonic imperfect consonances.
• The main dissonant suspension for a counterpoint melody to use below the cantus firmus is 2–3.
• The Consonant Suspension: The dissonant suspension has been emphasised here for the purpose of exploration and learning, however there is another type of suspension: The consonant suspension which, as you might guess, does not contain a harmonic dissonance on the strong-beat but rather a harmonic consonance. Thus, other motions like 5–6 or 6-5 are possible and may be used. However I suggest these be used more sparingly as the goal here in fourth species is to explore harmonic dissonance by way of the suspension technique. Note: A consonant suspension does not need to resolve downward so long as the move from the suspension into the weak beat is another harmonic consonance against the cantus firmus.

Using suspensions

The pattern set forward by a fourth species counterpoint line invites listeners to interpret the weak beats as the primary consonances, so treat suspensions in fourth species the same way you would treat their intervals of resolution in first species. Use 7–6 and 4–3 (above) or 2–3 and 5–6 (below) liberally, but not more than three times in a row (like thirds and sixths in first species). Since you cannot use two octaves or two fifths in a row in first-species, it is similarly avoided in fourth species and, as a result do not use two 9–8, 6–5, or 4–5 suspensions in a row. In fact, try to avoid any combination that would result in two harmonic fifths or harmonic octaves on consecutive weak beats in fourth species (known as after-beat fifths or octaves).

The Fourth Species Counterpoint Melody

When composing your counterpoint melody, try to use dissonant suspensions whenever possible. This will create a line consisting mostly of downward stepwise motion, and it will make it hard to direct motion toward a climax, but this is fine. Do not worry about the shape of the line so long as it is smooth and singable and the suspensions are properly prepared and resolved. It is often difficult to create a fourth species counterpoint with the same shape as a cantus firmus, and the main goal of fourth species is the treatment of the suspensions. If a dissonant suspension is not possible, you may use the above-mentioned “consonant suspension” to keep the line and flow moving without creating other voice-leading problems.

Beginning a fourth species counterpoint melody

Always begin with a half rest and then start your counterpoint melody above the cantus firmus with do, scale degree or sol, scale degree . Begin a fourth species counterpoint melody below the cantus firmus with do, scale degree .

Ending a fourth species counterpoint melody

There is only one option for ending fourth species: The cantus firmus must end with re–do, scale degrees , and the counterpoint melody will end with a dissonant suspension. The penultimate bar will contain do–ti, scale degrees , and the final bar will contain a whole note do, scale degree . The do–ti, scale degree motion will form a 7–6 suspension above the re, scale degree in the cantus firmus, or a 2–3 suspension below the re, scale degree in the cantus firmus. As a dissonant suspension, that do, scale degree will always be tied over from the previous bar.

Exception: Breaking the Chain

If neither a dissonant suspension of a consonant suspension is possible, especially if you encounter a larger problem (such as a potential voice-crossing, etc.), it is permissible to break the chain of suspensions that are characteristic in fourth species counterpoint. When you break the flow of suspensions, follow the principles of second-species counterpoint and try to resume fourth species suspensions as soon as possible. One short-term possibility is to leap or skip upward from a downbeat consonance to weak-beat consonance. At least one or two upward leaps will be necessary to counteract the downward resolutions in order to keep the line in a singable range. Try not to break species more than once per exercise, and if so, do it only for just a bar or two.