Introduction: Understanding Chord Borrowing

Chord borrowing is a harmonic technique used in tonal music that involves substituting a chord from a closely related key for another diatonic chord within a the key area of a secondary scale degree. This technique represents is a basic form of chord substitution. Unlike modulation, which aims to shift the key of the music either permanently or for a large portion or section, chord borrowing introduces chords from other keys without altering the original key or tonal center. Tonal music often explores different tonal regions while maintaining a connection to the main key and tonal center. Another term often used for a borrowed chord is applied chord.

Closely Related Keys

In the context of this discussion, a closely related key is defined as one associated with a secondary scale degree of the primary key, specifically degrees to . It’s important to note that the secondary scale degree in either the major or minor mode which forms a diminished triad (i.e. diatonic locrian mode) is not considered a stable tonal key and therefore is never used as a possible secondary key area.

The two charts below illustrate the secondary key areas for both major and minor modes, Additionally, borrowing from a secondary minor key area includes chords from the raised form of the minor scale.

Secondary Key Areas: Major Mode

Secondary Key Areas: Minor Mode

Chord borrowing serves various purposes, such as adding contrast, emotional depth, or color to the music. However, during the common practice period of Western tonal music, its use was often restricted to specific uses, such as the secondary dominant.

Voice-Leading Borrowed Chords

Borrowed chords will introduce one or more tones that do not belong to the primary key (i.e. non-diatonic to the primary key). Any non-diatonic tone should be introduced through diatonic melodic voice-leading, thinking at least locally within the context of the secondary key from which the chord(s) is borrowed. Except for the tritone, melodic intervals should be handled cautiously and you should avoid the use of augmented or diminished melodic intervals in your writing. Also, at this stage, chromatic voice-leading remains prohibited.

The Secondary Dominant

The secondary dominant refers to a Dominant chord, triad or seventh, borrowed from a secondary scale degree within the primary key. This chord functions similarly to how it would within its own key area, thus has a Dominant harmonic function relative to the secondary key. This process of locally emphasizing a secondary scale degree as a localized tonic is known as tonicization. Consequently, the chord progression involving a secondary dominant typically follows a common cadential pattern, such as that found in an Authentic Cadence (Dominant Tonic) or a Deceptive Cadence (Dominant Submediant or Subdominant). The resolution chord can be another borrowed chord or represent a return to a diatonic chord within the primary key.

The use of secondary dominants is quite common not only in classical music but in many popular and folk songs. For example, the opening of the Irish folk song “Danny Boy” features a secondary dominant to the SubDominant Major in the very first phrase:

Secondary Dominants in Major

The example below demonstrates the available secondary dominants in the major mode, using C major as the reference key. Here, all dominants proceed to the tonic in an authentic harmonic movement. This illustrates one possible approach, although alternative paths, such as the Deceptive cadential model, could also be used.

The introduction of these new chords is unproblematic as long as the voice-leading is handled properly and the chord’s functional role as a Dominant to the secondary key area is respected.

Secondary Dominants in Minor

The process of deploying secondary dominants in the minor mode is very similar to that of the major mode. A few of these secondary chords are already known by way of the raised form of minor. In this context, however, we are to treat these chords as secondary dominants with a dominant function in the secondary, tonicized key area. In the example below, we have the secondary dominants in minor and, as with the examples in the major mode above, all dominants proceed to the tonic in an authentic harmonic movement; alternative paths, such as the Deceptive cadential model, could also be used.

Since the minor mode has special voice-leading considerations with respect to the raised form of the mode, we do need to be mindful of this when using these chords in minor. However, when using secondary dominants in a progression, the guidelines for handling the pivot-tones in minor are superseded by the voice-leading guidelines found here.

Secondary Dominants: Basic Guidelines

1. Secondary Dominants can replace any diatonic triad or seventh chord, provided they tonicize a valid secondary key area relative to the primary key (consult the provided charts for clarity).
2. Integrate any non-diatonic tones from the borrowed chord through smooth diatonic melodic motion, avoiding augmented or diminished intervals, except for the tritone.
3. Handle non-diatonic tones similarly to pivot tones in the Minor Mode, especially the artificially introduced leading-tone of the secondary key area, which should ideally ascend to the tonicized secondary scale degree.
4. In the Minor Mode, the primary key’s pivot tone guidelines may be overridden by the above voice-leading requirements.
5. While the use of secondary dominants is at the composer’s discretion, moderation is advised so as not to destabilize the primary key. The use of many secondary dominants may necessitate a strong cadence to help firmly re-establish the primary key and restore balance.