One of the most puzzling questions for scholars of fifteenth and sixteenth-century music is how composers went about creating polyphonic compositions. The training in grammar and arithmetic was based on memorization. Training in music was based on exactly the same principles: students would begin by learning the musical gamut through the Hand. The most important part of counterpoint instruction consisted of the systematic memorization of interval progressions. The central fact about visualization of sights is that the pitch on which the added part is visualized through a number is then transposed up by a fifth, an octave, or a twelfth. Composers of isoryhthmic motets chose to organize their pieces in tightly organized structures because it allowed them to work out the pieces in their mind and make them memorable to performers. There is little doubt that oral composition continued throughout the sixteenth and seventeenth centuries. Writing did not replace oral composition, but could be used side by side with it.