If one reads the text-books of the seventeenth and eighteenth centuries it becomes obvious that in those days the practical knowledge of harmony and counterpoint was a sine qua non for all musicians. Most performers, indeed, of any reputation composed music habitually, either to play themselves, for teaching, or to make some profit from publication. It may be that this universal education in the making of music is one of the reasons for the astonishing amount of much more than tolerable music which has come to us from this period. Even singers, that variety of homo sapiens which is often classified apart, were so trained, if only to decorate the repeats of da capo arias with their ‘incredible graces’.