Pivot Chord Example
Answer: Sometimes people use these terms interchangeably, but I think it’s better to reserve the term “modulation” for a prepared key change, as opposed to an abrupt switch to a new key. Typically the modulation will involve a pivot chord that is found in both keys. For example, in C major one could write I, IV, V, I, ii, V, then alter the ii to a major triad or a major triad with a seventh. The new II7 chord now sounds like a V7 in the key of G, and the I that preceded it now seems like a IV in the new key – the I/IV is the pivot.
Chopin Nocturne in F Minor Op.55 no.1