“Tonality” is the sense of being in a particular key.
The tonic chord has the same function as the root note of a scale. It’s the place where things start and end, where “home” is, the context in which everything else relates. Especially the “leading tone” (seventh note in the scale)
All the notes of a scale have varying degrees of strengthening or weakening the relative gravity of the tonic.
BUT our “sense” of a key centre can be played with 🙂
1. New leading tones
Notes other than the tonic can be strengthened by introducing their respective leading tone (the 7th note in a scale, 3rd of any dominant chord, or the half step below a root)
This brings in a note outside the key and pull our ears to another potential note as the tonic. In other words, a sense of a second key can emerge.
If this continues to happens over a span of time along with creating strong chord resolution within the “new” key, then a full modulation happens and you have a new “home base”
Your ear may become used to the new key, but a lot of music resolves back to the original key by re-introducing the original notes… creating a wider experience of never having really “left”.
2. Borrowing chords
This is a very simple way to add some cool new harmonic interest to your chord progressions.
The most common place to borrow chords from is the parallel minor key.
e.g If you’re writing in a C major, you could borrow chords from the parallel C minor key.
3. Modal interchange
Another easy place to borrow chords from is from other modes that share the same tonic.
e.g If you in C major, check out chords from C Dorian or C Lydian…
You can also play around with the “identifier notes” of any mode to emphasize it with your leads. Like the #4 with Lydian or the minor 6th + major 7th in Dorian.