A C-major chord has the notes C, E, G chosen from the C major scale consisting of the notes C, D, E, F, G, A, and B. Major chords, in general are composed three notes – the root note, which is the tonic of the scale (U), and two other notes that are at an interval of a major 3rd (M3) and perfect 5th (P5). Looking at the C chromatic scale below, the notes of C major scale at intervals of 2-2-1-2-2-2-1 i.e. at (U,) M2, M3, P4, P5, M6, M7 and P8 (i.e. . 1-2-3-4-5-6-7-8) become obvious.
C,C#,D, D#,E, F, F#,G, G#,A, A#,B, c U–m2–M2–m3–M3–P4–TT–P5–m6–M6–m7–M7–P8
The C major chord is composed of the 1st 3rd and 5th notes of the C major scale, corresponding to the U, M3, P5 criteria above. Looking now, at the C major scale, the notes C, E and G at U, M3, and P5 (often written as 1-3-5 indicating the notes at unison-major 3rd and perfect 5th intervals) become obvious.
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