In fourth-species counterpoint, the counterpoint line and cantus firmus both move once per bar, but they are rhythmically offset from each other by a half note. (Think syncopation on the bar level.) The counterpoint line will be notated in half notes, with each weak-beat half note tied across the bar line to the following strong beat. This arrangement means that in pure fourth-species counterpoint, the two lines always move in oblique motion. It also introduces a new kind of dissonance: the suspension.

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. For the complete examples from Gradus ad Parnassum as exercises, solutions, and annotations, see Gradus ad Parnassum Exercises.

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 note in the counterpoint that is consonant with the cantus. This note is tied to the suspension, and the two are the same pitch.
• Suspension: a strong-beat note in the counterpoint, tied from the preparation, that is dissonant with the cantus.
• Resolution: a weak-beat note in the counterpoint that is one step below the preparation-suspension pitch and consonant with the cantus.

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

Types of suspensions

Suspensions are categorized according to the intervals of the suspension and resolution tones 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 down by step 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 (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 to imperfect consonances.
• The main dissonant suspension to use below the cantus firmus is 2–3.
• Other motions like 5–6 can be used, but they do not constitute dissonant suspensions, as the suspended note is not dissonant.

Using suspensions

The pattern set forward by a fourth-species line invites listeners to interpret the weak beats as the main 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 no 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, do not use two 9–8, 6–5, or 4–5 suspensions in a row. In fact, avoid any configuration that would create two fifths or two octaves on consecutive weak beats in fourth species (after-beat fifths or octaves).

The Fourth-Species Counterpoint Line

Use dissonant suspensions whenever possible. This will create a line consisting mostly of downward stepwise motion, and it will also make it hard to direct motion toward a climax, but this is fine. Do not worry about the shape of the line as long as it is smooth and singable and the suspensions are properly prepared and resolved. (It is 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, so we focus on that over melodic shape.)

If a dissonant suspension is not possible, try to use a tie from weak beat to strong beat. This can be a “consonant suspension,” or you can leap up from 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.

If neither a dissonant suspension nor a consonant tied figure is possible, it is permissible to break species (see video demo below). When you break species, follow the principles of second-species counterpoint and resume fourth-species ties as soon as possible. Try not to break species more than once per exercise, and do so for just a bar or two.

Beginning and Ending

Beginning a fourth-species counterpoint

Begin a fourth-species counterpoint above the cantus firmus with do [latex](\hat1)[/latex] or sol [latex](\hat5)[/latex]. Begin a fourth-species counterpoint below the cantus firmus with do [latex](\hat1)[/latex].

Always begin with a half rest.

Ending a fourth-species counterpoint

There is only one option for ending fourth species. The cantus firmus must end with re–do [latex](\hat2-\hat1)[/latex]. Do not use a cantus that ends with ti–do [latex](\hat7-\hat1)[/latex].

The counterpoint will end with a dissonant suspension. The penultimate bar will contain do–ti [latex](\hat1-\hat7)[/latex], and the final bar will contain a whole note do [latex](\hat1)[/latex]. The do–ti [latex](\hat1-\hat7)[/latex] will form a 7–6 suspension above the re [latex](\hat2)[/latex] in the cantus, or a 2–3 suspension below the re [latex](\hat2)[/latex] in the cantus. As a dissonant suspension, that do [latex](\hat1)[/latex] will always be tied over from the previous bar.

Demonstration

Examples 3 and 4 are video lessons by Kris Shaffer illustrate the process of composing a fourth-species counterpoint above and below a cantus firmus. These videos provide new information about the compositional process, as well as concrete examples of the above rules and principles.

Example 3. Composing fourth-species above a cantus firmus.

Example 4. Composing fourth-species below a cantus firmus.

1. For the complete set of Fux exercises, see the Gradus ad Parnassum chapter.