Third [Example 1: opening, Beethoven: Fifth Symphony, 1st mvt] The third is a musical interval. Within the tonal system of music, it is an interval of special importance, since it has great power to influence the character and expressive nature of that music.
The Interval of the ThirdThe third comprises two tones that are three tones apart: There are in practice two important kinds of third: major and minor. The Major ThirdThe major third sounds as follows, played here first one note after the other (as in a melody), and then simultaneously (as in a chord). [Example 2: the major third sounded (1) successively, (2) simultaneously] The interval sounds smooth and free of tension. That is to say, it is a consonant interval. It conveys a feeling of stability. The distance between the two notes of a major third comprises two whole-steps. 2 whole-steps (= 4 half-steps ) The Minor ThirdThe minor third sounds as follows. [Example 3: the minor third sounded (1) successively, (2) simultaneously] Like the major third, this interval sounds smooth and free of tension - consonant - though it perhaps sounds a little less out-going, a little more somber, than the major third. The distance between the two notes of a minor third comprises one whole-step and one half-step. 1 whole-step + 1 half-step (= 3 half-steps ) (Incidentally, note that all musical intervals are counted inclusively. That is, the first and last notes are both counted. As a result, all intervals comprise one step less than their number might seem to indicate. A third thus contains three tones, but only two steps.) There are two other kinds of third, augmented, and diminished, but these need not concern us here. (They are demonstrated in Interval.)
The Third in MelodyThe third plays a crucial role in tune and melody. Sing the first five tones of The Star-spangled Banner silently to yourself now. The tones that you just sang are all a third apart from each other; in other words, each time you leapt from one tone to the next, you leapt the interval of a third. But let us go back to the first musical example of this definition: the well-known opening of Beethoven's Fifth Symphony. Each of the two phrases consists of four tones. The first three are all at the same pitch, then there is a drop. That drop is in each case a third: [Example 4: Beethoven: Fifth Symphony, 1st mvt: first two phrases]
As you can see from the diagram, the first drop is a major third, the second a minor third. These two phrases, which together form a motive, are repeated many times during the symphony, often with the thirds expanded or contracted to other intervals.
The Role of the Third in Tonality
The third is of critical importance to the key system of modern musical tonality. It is capable of exerting strong influence on the character of both melody and harmony in tonal music, hence of affecting the emotional expression of a whole passage, even of an entire composition. The third plays an especially important role in the triad - the basic chord of tonal harmony. The triad consists of three tones. In its primary form, the triad comprises two intervals of a third piled on top of one another: Whether each of these thirds is major or minor entirely determines the character of the triad itself.
The Third in the Major and Minor TriadsThe two most frequently used triads each consist of one major third and one minor third. These are:
Let us convert these into sound now. The major triad (in the left-hand diagram) sounds as follows, first successively, then with the notes between them, then simultaneously: Now the minor triad (in the right-hand diagram) sounded in the same way: Of these, the major triad has the brighter sound, the minor triad the duller one. [Example 7: (1) major triad, (2) minor triad, repeated] As you can see and hear, the type of triad is determined by the type of third in the lower half of the triad. If the lower third is major, then the triad itself is major; if the lower third is minor, the triad itself is minor.
The Third in the Diminished and Augmented TriadsThis is not the case with the other two types of triad: the diminished and augmented triads. Instead of containing one of each type of third, as did the major and minor triads, these types contain two of the same type of third:
These two triads sound as follows: the diminished triad: and now the augmented triad: As you can hear, the four triads sound very different from one another. So you can imagine that a passage of music in which one of the four predominates will itself take on the character of that triad: a passage with more major triads will itself sound "major"; one with more diminished triads will sound "diminished," and so on. From this you can perhaps imagine how greatly the third influences the character of a piece of music. In tonal music of the late Baroque, the Classical Era, and the Romantic Era, the third exerts its most powerful influence on a piece through that piece's tonic triad. The tonic triad must be either major or minor. If the tonic triad is major, then the piece itself is said to be "in the major key" [Example 10]; if the tonic triad is minor, then the piece is said to be "in the minor key" [Example 11]. Finally, it is very common to hear a melody sung simultaneously at two different pitch-levels, one a third higher than the other. This is called singing in thirds. We find it in Africa, in the folk music of many places, and in popular music. Here is an example that will probably be familiar to you - the thirds are mixed with an occasional fourth. [Example 12: Simon and Garfunkel: "Wake up, Little Suzy"]
Summary:
Note: Having learned about the third, you may want also to consult the definition of the Sixth, since the sixth is closely related to the third (they are in fact the inverse of one another), and the two behave quite similarly.
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