there are 3 basic types of harmonies: (some may disagree, but I offer this as an example only)

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CHORDAL harmonies are based on the current chord, and the harmony note is generally any other note in the current chord besides the melody note. The variations in chordal harmonies come from placement of the harmony note in relation to the melody (above or below). The examples Mac gave are all options used in chordal harmonies. Chordal harmonies tend to be less active than other harmonies, because the harmony note doesn't have to change every time the melody note changes... it just has to be in the current chord.


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SCALIC harmonies are based on the song's key. Scalic harmonies tend to pick one or more notes in the scale and consistently add that note to the melody note.

Let's call the scale Do Re Mi Fa So La Ti Do. a "Thirds" harmony would work like this:
melody / harmony
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Do / Mi
Mi / So
La / Do
(1st) / (3rd)

a "fifths" harmony would work like this
melody / harmony
------------------
Do / So
Mi / Ti
(1st) / (5th)

the actual notes used would depend on the key
This type of melody is very active because the harmony note changes every time the melody note changes.

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I don't remember the third kind, but I bet others here will know.

https://www.dropbox.com/sh/ey71h8ep047758h/AAC12jNM0Hz9Q8zsh5iDeqNHa?dl=0