You can sing or play this through forward and then backward, and its counterpoint remains correct. They had also the inverted canon, in which the second part consisted of the first part turned upside down. The canon by augmentation makes the melody appear in a subsidiary part in notes longer than those in which it appeared in the principal part; and the canon by diminution is formed on the opposite principle. These old musical puzzle-workers had other forms far more complicated, and they took great delight in writing "riddle" canons. In these only the subject was given, with the motto, "Ex una, plures," meaning that the musician must work out the other parts from the one; and then some hint as to the manner of working them out would be given, as, "Ad medium referas, pauses relinque priores." The working out of these riddle canons became a mania with Okeghem and his immediate successors; and the result was that they acquired an immense command over the technics of contrapuntal writing. But "the highest praise that can be awarded to their works is that they are profound in their scholarship, not without evidences of taste in the selection of the formulas to be employed, and certainly imbued with a good deal of the dignity which would inevitably result from a skilful contrapuntal treatment of the church chant." It is, however, of singular significance in the history of this period that some of the works of both Hobrecht and Brumel show a tendency toward some conception of chord harmonies. Here is an example, which looks modern:-- BEGINNING OF A MOTET BY BRUMEL. (From Naumann's "History of Music.") [Music: O Do-mi-ne Je-su Christ . . . . . e.]