It is a little harder to see the chords in melodies that include notes that are not meant to be part of the harmony. Such notes are called nonharmonic tones, also called nonchordal tones. These will be discussed in more detail in chapter 13, but for the moment it is enough to know that nonharmonic tones usually move by step to a note that is part of the chord.
Nonharmonic tones that come in rhythmically strong positions -- for example, on a metric accent or on the first part of a beat subdivision -- are called accented nonharmonic tones. These generally move downward by step to a chord tone. Unaccented nonharmonic tones can be found moving either up or down, but again will almost always move by a step to a note that is part of the chord. So if the movement of the melody is upward by step the accented notes are probably part of the chord; if the movement is downward by step the accented notes may or may not be part of the chord, as in figure 18.
It helps in these ambiguous cases to know that most melodies have a slow harmonic rhythm: chords will generally change only twice a bar in 4/4 or even less often. When they do change, the change will almost always occur on the notes with the strongest metric accent: the first beat of the measure, or possibly also the third beat of a 4/4 measure and the first or second beats in a 6/8 measure. In the above example the chord changes twice, both times on the strongest beat of the bar. With a typically slow harmonic rhythm a group of sixteenth notes or eighth notes moving stepwise must include some nonchordal tones, since you won't be able to change chords fast enough to agree with all of them. The last beat of the above could harmonize with a V chord (D major), which would make the two Gs (instead of A and F) into nonharmonic tones. However, following the principle of changing chords only when necessary and preferably on the strongest beats, the G major triad holds until the end of that bar and will change on the following downbeat.
Finally, it is essential to know the typical chord progressions. The F sharp and D in measure two of figure 15 could be part of the iii chord or the V, but your first guess should always be the stronger and more common progression, which in this case would be I-V. Also, you can look ahead and see that the following chord is again going to be I -- and a I-V-I would make much more sense than I-iii-I.