Musical note indicated by placing the symbols in the key signature, which then apply implicitly to all occurrences of corresponding notes. Explicitly noted accidentals can be used to override this effect for the remainder of a bar. A special accidental, the natural symbol , is used to indicate an unmodified pitch. Effects of key signature and local accidentals do not accumulate. If the key signature indicates G, a local flat before a G makes it G (not G), though often this type of rare accidental is expressed as a natural, followed by a flat () to make this clear. Likewise (and more
Key signature sometimes is this change indicated with a change of key signature; if not, the passage in the second key will not have a matching key signature. The Toccata and Fugue in D minor, BWV 538 by Bach has no key signature, leading it to be called the "Dorian", but it is still in D minor; the Bs that occur in the piece are written with accidentals. Keys which are associated with the same key signature are called relative keys. When musical modes, such as Lydian or Dorian, are written using key signatures, they are called "transposed modes". Exceptions to common-practice-period