A Working Method for Identifying Modulations

1.  Ring all the accidentals in the passage

2.  Consider whether each accidental raises or lowers the note it is attached to

• If it raises the note, treat that note as a possible leading note, leading by step upwards to a new tonic
• If it lowers the note, treat that note as either the subdominant or the submediant in the new key

3.  Examine the bass line below the accidental

• Look for evidence of a V - I or V - Ib progression
• Even if the music does not come to a cadence, such a progression can confirm the transitory existence of a new key (a transitory or passing modulation)

4.  Decide whether the new key is major or minor

• In principle, this question can always be answered by consulting Riepel's 'Household' of Keys. However, as you may well ahve to deal with music written in a later period than Riepel's book, when the options are greater, it is always sensible to check the major / minor aspect of any new key.
• Simply look carefully at the new tonic chord (the one you have identified with a I or Ib) and see whether it is major or minor

FURTHER GENERAL INFO:

• Music in a major key is likely to modulate first to the dominant
• Music in a minor key is likely to modulate first to its relative major, though it sometimes modulates first to its dominant
• Whatever the other structural forces at work in Western music of the tonal era, there is generally one underlying structure - movement away from the tonic, and, at some later point, movement back to the tonic. In both major and minor keys the movement back to the tonic will usually be signalled by the prominent use of the dominant note or chord.