Barron's AP Music Theory Chapter 5: Harmonic Organization I: Intervals, Triads, and Seventh Chords

Harmony

the way notes are simultaneously sounded creating a vertical element to music

counterpoint

a single melody line or linear voice added to another line or voice

interval

distance between two pitches. described by quantity (size) and quality.

melodic interval

Two notes sounded separately

harmonic interval

two notes sounded together

diatonically

Between notes within the same key or tonality

enharmonic intervals

sound the same but are spelled differently and therefore function differently

doubly augmented

When a major or perfect interval is made one whole step larger without changing the letter names of the pitches

doubly diminished

When a minor or perfect interval is made one whole step smaller without changing the letter names of the pitches

simple intervals

intervals that are one octave or smaller in quantity

compound intervals

intervals that are larger than an octave

inverted interval

transferring the lower note an octave higher or transferring the higher note an octave lower

the rule of nine

when any simple interval is inverted the sum of the ascending and descending intervals must add up to nine

consonant intervals

P1 and P8 (most stable consonances)
P5, M3, m3, M6, m6
(sometimes P4)

dissonant intervals

M2, m2, M7, m7, all augmented and diminished intervals and sometimes P4 (which is generally considered a dissonance when used harmonically above the bass)

resolution

the motion of the dissonant interval to the consonant that acts as its goal

triad

a three-note chord made up of two intervals stacked in thirds

tertian harmony

harmony built on thirds, used during the Common Practice Period

seventh chord

Contains four notes: A root, third, fifth, and seventh
* seventh chords are considered dissonant