How does one analyze a song that moves primarily between two non-diatonic chords?

1. How do you use non diatonic notes?
2. How do you know what key a song is in by chords?
3. What are diatonic chords?

How do you use non diatonic notes?

The best way to add non-diatonic chords to a chord progression is by using a common note from the diatonic chord into the non-diatonic chord, which smoothes an otherwise abrupt change. That's what happens in the Fmaj → Dmaj, where the common note is A.

How do you know what key a song is in by chords?

To find the key from a chord progression, do the following:

1. Write down all of the chords.
2. Write down the scales associated with each chord. (ie: If you have E minor, write down the E minor scale. ...
3. Look at each scale and see if the chords' root notes are within that scale. If they are, that is the key you are in.

What are diatonic chords?

The word 'diatonic' simply means 'within a key', so a diatonic chord progression is a set of chords made up of notes from within a key signature. Listen up: scales aren't just torture devices invented by guitar teachers... When you use a scale, say, C major, you are playing 'in the key of C'.