Final answer:
The composer and poet of the ars nova period was Guillaume de Machaut. He played a crucial role in the shift towards more complex polyphony in music, paralleling transitions in art that emphasized clarity, harmony, and beauty.
Step-by-step explanation:
The notable composer and poet of the ars nova, also known as the 'new art' period, was a) Guillaume de Machaut. Machaut was one of the key figures in the transformation of music during the Medieval period, particularly known for his stylized use of motets and his contribution to polyphony. Unlike other options like Johannes Ockeghem, Hildegard of Bingen, and Leonin, Machaut's works are quintessential exemplars of the ars nova period which marked a significant shift towards the use of thirds considered previously as dissonances, embracing a more complex and elaborate polyphonic style in music composition. The increased vocal range in this era facilitated smoother transitions and less crossing of parts compared to earlier medieval music, which had a more narrow vocal span and thus greater contrast was necessary amongst vocal parts.
Machaut’s contribution to music mirrors the developments in arts during this time, as seen in the works of painters such as Nicolas Poussin and Claude Lorrain in the following century, who emphasized clarity and order, and Georges de la Tour, who was known for his religious chiaroscuro scenes. The renaissance brought about a transformation in many artistic fields, culminating in the production of art and music that resonated with emerging humanist ideas and embraced a heightened aesthetic of beauty and harmony.