Carlos S. answered 03/27/20
Effective and resourceful Guitar and Music Production Tutor
Hi! You can think of it as every song as a Modal piece of Music
Music works/songs using the I degree chord of the Natural Major Scale as its tonal center is what we know as "major songs".
Songs using the VIm degree of the same scale as a tonal center can be considered as "minor songs" (this is. songs that use the VI degree as the new Root)
Note: you will still need to add a "7" chord in the V degree of that minor scale (this will be "dominant" chord to make the song "pure minor, because you need it to resolve over the Im chord -our old VI chord-)
Those Major and minor examples are considered MODAL already: Major = Ionian mode (based on the I degree) and Minor = Aeolian Mode (based on the VI degree).
Then, you have other MODES. For example, if you take the chord from the II degree of the scale for your tonal center, that would be a DORIAN song (minor with a major 6th). If you use the V degree, that would be a MIXOLYDIAN song (Blues-related), an so on it goes with each of the chords derived from all 7 notes in the scale.
If you are interested in learning harmony, we could have lessons with cool interactive harmony practice materials!
Have a great night
Carlos