Fourth-Species Counterpoint

Fourth-species counterpoint introduces suspensions — the most expressive dissonance treatment in tonal counterpoint. The counterpoint moves in half notes but is offset from the cantus firmus by a half note, so each new note is tied across the barline. The tied note, called the suspension, sits on the strong beat where it is temporarily dissonant against the cantus, creating tension before it resolves by step downward to a consonance on the weak beat. This three-phase process — preparation (consonant), suspension (dissonant), resolution (consonant) — defines the suspension figure.

The most important suspensions in two-voice counterpoint above a bass are the 7-6, 4-3, 9-8, and 2-1 (or their octave equivalents). When the counterpoint is below the cantus, the 2-3 suspension (resolving upward) is characteristic. Suspensions must resolve downward by step in most cases; the 2-3 resolves upward because the bass voice is moving toward a fuller sound. It is possible to "break" the chain of ties occasionally by inserting a consonance on a downbeat (a "consonant fourth species" moment), but the suspension texture should predominate.

The emotional power of fourth species comes from the delay: the counterpoint lags behind the cantus, arriving on a dissonance precisely when the harmonic rhythm suggests resolution. This rhythmic displacement — called syncopation — gives fourth species its characteristic feeling of yearning and release. Suspensions became one of the primary expressive tools of Renaissance and Baroque music, appearing in madrigals, motets, and instrumental works wherever heightened emotion or climactic moments require intensified dissonance.