Step 2. Leading Notes
In a three-part texture like a Trio Sonata, the leading note will normally rise by a semitone to the tonic, even in an inner part.
The leading note occurs in chords V, V7 and vii°. The tonic occurs in chords I or VI. Be aware of modulations, so that you always know what the current leading note is. Rise to the tonic when the chord changes, not before! (NB: If the leading note moves to a chord without a tonic in it, this rule does not apply).
The leading note is normally sharpened with an accidental in a minor key, and the accidental appears in the figure. Occasionally the leading note is not sharpened (e.g. descending melodic minor scale). Do not sharpen it, if the figure does not tell you to.
Be careful to avoid the augmented 2nd step between the 6th degree of the scale and the leading note (e.g. F-G#, in A minor), when moving towards the leading note.
Place the leading note and tonic in the same part. Use the part which allows the smoothest voice leading (avoid unnecessary leaps).
Here is an example. At ②, the chord is G major (V). It must contain a leading note (B).
We should write this into the middle part (to avoid a leap in the top part), and then follow it with a tonic C in the same part.
In the next example, the key has been A minor, but we now see a D# and F# at ②. The chords are Am, B, Em so this is a modulation to E minor, and the new leading note is D#. At ② we need to write the D# into the top part, to avoid an augmented 2nd from C-D# in the middle part. D# then moves to E at ③.
Here are some examples to try. Find the leading notes, and then resolve them to their tonics.
Here is the solution: