Diatonic harmony forms the backbone of Western tonal music. It involves chords built on major and minor scales, creating a framework for musical analysis and composition. Understanding diatonic harmony is essential for musicians across genres, from classical to jazz and pop.

This topic covers triads, Roman numeral analysis, common chord progressions, and voice leading principles. It also explores cadences, seventh chords, and secondary dominants. These concepts help musicians create smooth, logical harmonic progressions and analyze existing works.

Diatonic harmony in major and minor keys

• Diatonic harmony is the foundation of Western tonal music and involves chords built on the notes of a major or minor scale
• Understanding diatonic harmony is crucial for analyzing, composing, and performing tonal music across various genres and styles

Triads built on scale degrees

• Triads are three-note chords constructed by stacking thirds on each scale degree of a major or minor scale
• In major keys, the triads built on scale degrees are: I (major), ii (minor), iii (minor), IV (major), V (major), vi (minor), and vii° (diminished)
• In minor keys, the triads are: i (minor), ii° (diminished), III (major), iv (minor), v (minor), VI (major), and VII (major or diminished, depending on the type of minor scale)

Roman numeral analysis

• Roman numeral analysis is a method of labeling chords based on their scale degree and quality
• Upper-case Roman numerals (I, IV, V) represent major triads, while lower-case numerals (ii, iii, vi) represent minor triads
• Diminished triads are denoted with a degree sign (vii°), and augmented triads with a plus sign (III+)
• Roman numeral analysis helps identify chord functions and progressions within a key

Common chord progressions

• Certain chord progressions are frequently used in diatonic harmony due to their strong sense of tonality and resolution
• The I-IV-V-I progression is a fundamental chord sequence found in countless pieces of music (blues, rock, folk)
• The ii-V-I progression is common in jazz and popular music, often used for turnarounds and cadences
• Other common progressions include I-vi-IV-V, I-iii-vi-ii-V, and I-V-vi-IV

Tonic, dominant, and predominant functions

• Chords in diatonic harmony have specific functions that contribute to the overall sense of tonality and tension-resolution
• Tonic function (I chord) provides a sense of stability and resolution, often used at the beginning and end of phrases
• Dominant function (V chord) creates tension and drives the harmony towards resolution to the tonic
• Predominant function (ii, IV, vi chords) precedes the dominant and builds tension, setting up the resolution to the tonic

Voice leading in diatonic harmony

• Voice leading refers to the smooth and logical movement of individual voices (soprano, alto, tenor, bass) within a harmonic progression
• Proper voice leading enhances the clarity, coherence, and expressiveness of diatonic harmony

Smooth voice leading principles

• Aim for the smallest possible motion between chords, preferring stepwise motion or common tones
• When voices must leap, use consonant intervals like thirds and sixths
• Resolve tendency tones (leading tone, chordal seventh) according to their natural inclinations
• Maintain independence of voices by avoiding parallel motion in perfect intervals

Avoiding parallel fifths and octaves

• Parallel fifths and octaves between two voices are generally avoided in traditional voice leading
• These parallel intervals can create a lack of independence between voices and undermine the harmony
• To avoid parallel fifths and octaves, use contrary or oblique motion, or have one voice move by step while the other leaps

Tendency tones and resolutions

• Tendency tones are notes within a chord that have a strong pull towards specific resolutions
• The leading tone (7th scale degree) has a strong tendency to resolve upward to the tonic
• The chordal seventh (7th of a seventh chord) tends to resolve downward by step
• Properly resolving tendency tones helps create a sense of tension and release in diatonic harmony

Chord inversions and bass lines

• Chord inversions occur when a chord's bass note is not the root, resulting in a different voicing and bass line
• First inversion (3rd in the bass) and second inversion (5th in the bass) are common in diatonic harmony
• Inversions can smooth out the bass line, create variety, and enable better voice leading between chords
• Carefully chosen inversions can also emphasize certain chord tones or create specific melodic patterns in the bass

Cadences in diatonic harmony

• Cadences are specific chord progressions that create a sense of ending or punctuation in a musical phrase
• Different types of cadences have varying levels of finality and are used to structure and delineate musical ideas

Authentic cadences: perfect vs imperfect

• Authentic cadences move from the dominant (V) to the tonic (I) chord
• Perfect authentic cadence (PAC): V to I, with both chords in root position and the tonic in the soprano
• Imperfect authentic cadence (IAC): V to I, but with one or both chords inverted, or the tonic not in the soprano
• PACs create a strong sense of resolution and finality, while IACs are less conclusive

Plagal cadences

• Plagal cadences move from the subdominant (IV) to the tonic (I) chord
• Often referred to as the "Amen" cadence due to its frequent use in church music
• Plagal cadences have a softer, more relaxed sense of resolution compared to authentic cadences

Half cadences and deceptive cadences

• Half cadence (HC): ends on the dominant (V) chord, creating a sense of incompleteness and anticipation
• Deceptive cadence (DC): moves from the dominant (V) to a chord other than the tonic (often vi), "deceiving" the listener's expectations
• HCs are used to create a sense of suspense or to mark the end of an antecedent phrase
• DCs can add variety, surprise, and harmonic interest to a progression

Cadences as phrase endings

• Cadences are essential for shaping the structure and flow of musical phrases
• They help define the boundaries between phrases, sections, and movements
• The type of cadence used can convey different levels of finality, from the strong closure of a PAC to the open-ended feeling of an HC
• Effective use of cadences contributes to the overall coherence and expressiveness of a musical composition

Diatonic seventh chords

• Diatonic seventh chords are four-note chords built by stacking thirds on each scale degree of a major or minor scale
• These chords add richness, complexity, and additional tension-resolution possibilities to diatonic harmony

Types of seventh chords

• Major seventh (maj7): built on the I and IV scale degrees in major keys (Imaj7, IVmaj7)
• Dominant seventh (V7): built on the V scale degree in major and minor keys, contains a major triad with a minor seventh
• Minor seventh (min7): built on the ii, iii, and vi scale degrees in major keys (ii7, iii7, vi7) and on the i and iv scale degrees in minor keys (i7, iv7)
• Half-diminished seventh (ø7): built on the vii scale degree in major keys (viiø7) and on the ii scale degree in minor keys (iiø7), contains a diminished triad with a minor seventh
• Diminished seventh (dim7): built on the vii scale degree in minor keys (vii°7), contains a diminished triad with a diminished seventh

Dominant seventh chords and resolutions

• The dominant seventh chord (V7) is the most important and frequently used seventh chord in tonal music
• It consists of a major triad with a minor seventh above the root, creating a strong sense of tension and desire for resolution
• V7 chords typically resolve to the tonic (I) chord, with the chordal seventh resolving downward by step
• The resolution of V7 to I is a defining feature of tonal harmony and is used in various cadences and progressions

Non-dominant seventh chords

• Non-dominant seventh chords (ii7, iii7, vi7, viiø7 in major; i7, iiø7, iv7, VI7 in minor) add color and variety to diatonic harmony
• These chords often serve predominant or tonic functions, depending on their scale degree and context
• Non-dominant seventh chords can be used for smooth voice leading, creating stepwise motion between voices
• They also enable the creation of extended harmonic progressions and sequences

Seventh chord inversions and figured bass

• Like triads, seventh chords can be inverted to create different voicings and bass lines
• Seventh chord inversions are labeled using figured bass, which indicates the intervals above the bass note
• First inversion (6/5): 3rd in the bass, figured bass is 6/5
• Second inversion (4/3): 5th in the bass, figured bass is 4/3
• Third inversion (4/2): 7th in the bass, figured bass is 4/2
• Inversions of seventh chords can facilitate smoother voice leading and create more interesting bass lines

Secondary dominants and tonicization

• Secondary dominants are dominant seventh chords that temporarily tonicize a non-tonic scale degree within a key
• They add harmonic variety, color, and tension to diatonic progressions, creating brief moments of tonal instability

Secondary dominant function

• A secondary dominant acts as a temporary dominant (V) chord to a non-tonic scale degree
• It creates a momentary sense of resolution and tonal center around the tonicized chord
• The most common secondary dominants are V/V (five of five), V/ii, V/iii, V/iv, and V/vi

Tonicization vs modulation

• Tonicization is a brief, temporary emphasis on a non-tonic scale degree, usually lasting for a few chords
• Modulation is a more permanent change of key, involving a cadence in the new key and a longer-lasting tonal center
• Secondary dominants create tonicization, while modulation requires additional harmonic and melodic changes to establish the new key

Common secondary dominants

• V/V: the most frequently used secondary dominant, resolving to the dominant (V) chord
• V/ii, V/iii, V/iv, V/vi: secondary dominants resolving to the ii, iii, iv, and vi chords, respectively
• These secondary dominants add harmonic interest and variety to diatonic progressions, often appearing in sequences or as embellishments

Resolving secondary dominants

• Secondary dominants typically resolve to the chord a fifth below (just like a regular V7-I resolution)
• The chordal seventh of the secondary dominant resolves downward by step to the third of the tonicized chord
• Proper voice leading principles, such as avoiding parallel fifths and octaves, should be observed when resolving secondary dominants
• After the resolution, the harmony usually returns to the original key, continuing the diatonic progression

Harmonic analysis and part-writing

• Harmonic analysis involves identifying and labeling chords, progressions, and cadences in a musical composition
• Part-writing is the practice of creating or arranging music for multiple voices or instruments, following principles of voice leading and harmony

Harmonizing melodies with diatonic chords

• To harmonize a melody, assign appropriate diatonic chords to each melody note based on the key and harmonic rhythm
• Consider the melody's contour, phrasing, and cadences when choosing chords
• Use a variety of chords and progressions to create interest and support the melody's expressive content
• Ensure smooth voice leading between chords and avoid excessive leaps or awkward intervals in the accompanying voices

Realizing figured bass with proper voice leading

• Figured bass notation indicates the intervals to be played above a given bass line, often in Baroque-style keyboard music
• To realize a figured bass, construct chords based on the figures and the bass note, following voice leading principles
• Pay attention to the resolution of tendency tones, proper treatment of dissonances, and avoiding parallel fifths and octaves
• Aim for a smooth, musical realization that supports the bass line and creates a coherent harmonic progression

Analyzing harmonic progressions in repertoire

• When analyzing the harmony of a musical composition, identify the key, chords, and progressions used
• Label chords using Roman numerals, figured bass symbols, or chord names (e.g., I, V6/5, Cmaj7)
• Identify cadences, secondary dominants, modulations, and other harmonic devices
• Consider how the harmony relates to the melody, form, and expressive content of the piece
• Use your analysis to gain a deeper understanding of the composer's harmonic language and musical style

Composing with diatonic harmony

• Apply your knowledge of diatonic harmony, voice leading, and harmonic progressions to create original compositions
• Start with simple chord progressions and melodies, gradually expanding to more complex harmonies and forms
• Experiment with different chord voicings, inversions, and non-chord tones to add variety and interest
• Use secondary dominants, tonicization, and modulation to create harmonic contrast and development
• Consider the expressive and emotional qualities of different harmonic choices, and use them to convey your musical ideas effectively