Theory 139 Laboratory September 4th, 2025 - Triads and Intervals: Quick Review

Triads: definition and role

• Triad: a sonority of three notes stacked in thirds: root, third, fifth. Top note is the fifth above the root.
• In close position, triad tones lie on adjacent lines or adjacent spaces on the staff.
• The tonic triad: triad built on scale degree 1 of a key (root on 1).
• Example tonic triad in C major: C – E – G; in F# major: F# – A# – C#.

Intervals: size, quality, and within the tonic triad

• Interval concept:
  • Interval size = number of scale steps between pitches. Example: C to E spans 3 scale steps.
  • Interval quality = number of semitones within those steps.
• Common interval qualities (in semitones):
  • Major third: $4$ semitones
  • Minor third: $3$ semitones
  • Perfect fourth: $5$ semitones
  • Perfect fifth: $7$ semitones
  • Octave: $12$ semitones
• Tonic triad in a major key (root 1, third 3, fifth 5):
  • 1 to 3 = $ext{Major Third}$
  • 3 to 5 = $ext{Minor Third}$
  • 1 to 5 = $ext{Perfect Fifth}$
• Melodic interval vs. harmonic interval: same interval types, but sound in time vs. simultaneously.

How to identify triads and intervals on the staff

• Triads can be identified by their close-position layout: adjacent lines or adjacent spaces on the staff.
• Within a tonic triad, you can locate consonant intervals: major third, minor third, perfect fourth, perfect fifth, octaves.
• Interval recognition rule (crisp):
  • Interval size depends on scale-step distance.
  • Interval quality depends on semitone count within those steps.
• Descending intervals can differ in perception; practice both ascending and descending forms.

Practice targets from today

• Focus on tonic triad in keys you’re using: identify 1–3–5 relationships and sing through related intervals.
• Practice octave transfers within the triad: recognize and sing phrases that span octaves of the same chord tones.
• Leaps within the melodies: recognize how leaps between scale degrees produce major or minor thirds depending on direction:
  • 5 to 3 (within the tonic triad) = minor third
  • 3 to 1 (within the tonic triad) = major third

Sight-singing and melodic procedures

• Core strategy for sight-singing melodies with tonic triad:
  • Identify the key.
  • Spell the tonic triad on the staff (1–3–5).
  • Scan the melody for notes belonging to the tonic triad and sing those first.
  • Use movable do and conduct in tempo; do not rely on a metronome during the performance.
• Tempo expectations: perform melodies and scale-degree patterns at the approved daily tempo.

Homework and next steps

• Homework 2 (due in one week): two activities
  • Activity 1: Naming keys and intervals.
  • Activity 2: Sight-singing, one in treble clef and one in bass clef.
• Note on practice tools: you may rehearse with a metronome beforehand, but do not perform with a metronome during the assignment.
• Melody to prepare next: Melody 3.36 (in Week 2 materials). Be ready to perform in class on Tuesday.
• Resources:
  • Check Canvas announcements for office hours, tutor info, staff paper, syllabus resources, and room changes.
  • Obtain a textbook or access the PDF in Week 2 materials (3.36 is included).

Quick recap points for last-minute review

• A triad is built by stacking notes in thirds: root – third – fifth.
• The tonic triad in major keys has: 1–3 as a Major Third, 3–5 as a Minor Third, and 1–5 as a Perfect Fifth.
• Interval size vs. quality: size = scale steps; quality = semitone count (e.g., Major Third = 4 semitones).
• Close-position triads place tones on adjacent staff positions.
• Practice modules: identify tonic triad in keys, sing intervals within the triad, and apply to melodies with moves between thirds, fourths, fifths, and octaves.