2 can be harmonized with the super tonic triad or seventh chord.
NOTE: In minor keys, remember that the supertonic triad must be found in first inversion because of the diminished fifth.
The only time you may use ii° is when it is preceded by ii°6 or iv and if it falls on a weak beat.
DOUBLING: In major keys you may double anything, although doubling the root or third is best. In minor keys, doubling the third ( 4 ) is best since it is not part of the tritone. However, if you must, you may double the root or fifth.
NOTE: When you precede this chord with the same harmony (e.g. ii ii6 or ii°6 ii°), make sure that the first chord occurs on a strong beat (i.e. do not separate these chords with a bar line).
* When a chord appears in parentheses, it must be used in prolongation (e.g. ii (I) ii6).
NOTE: In major keys, ii7 may contain doubled root ( 2 ) and omitted fifth ( 6 ) in root position only; however, in minor keys, you may not double or omit anything in ii∅7 because the fifth is diminished, not perfect.