@classmethod
def _fetch_key_signature(cls, tonic, quality):
    """ Returns a list of strings with the note names that make up the scale's key signature. """
    qualified_tonic = tonic + (' MINOR' if 'MINOR' in quality else ' MAJOR')
    key_signature_number = cls._KEY_SIGNATURE_NUMBERS[qualified_tonic]
    return tuple(cls._KEY_SIGNATURES[key_signature_number])
