A common replacement for the IV or ii
chord, the neapolitan chord is a
major triad based on the flatted second
scale degree (sometimes called II in
phygrian mode). Most often, it is seen in
first inversion, but can sometimes pop up in
root position. As such, the neapolitan chord is most commonly spelled IV bVI bII:
example in C major, and resolution to V
--------------------
----bo--------------
-------------o------
bo
-------------o------
o
--------------------
C: N6 V
As you can see, the
root (Db) and the
fifth (Ab) tend to resolve down to
chord tones in the V chord. To illustrate this, I left out the fith scale degree of the V chord (the root of the N6 chord will rarely move up by step to the fifth of V. Why? Who the hell knows?); you can also imagine that there is a fifth scale degree, if that makes you sleep better at night.
Also, if we're doing 4 part voicing, we tend to double the third (usually in the
bass) of the neapolitan chord instead of the more active-sounding root (bII) and fifth (bVI).