Final answer:
The Caput Mass giving birth to the contratenor bassus that generated four-part harmony was a matter of circumstance in the context of Renaissance music, which saw an increasing reliance on the interval of the third and the development of the madrigal form.
Step-by-step explanation:
The Caput Mass giving birth to the contratenor bassus that generated four-part harmony was a matter of circumstance in the context of Renaissance music. During this period, there was an increasing reliance on the interval of the third in music, which allowed for more elaborate polyphony.
The development of the madrigal form and the increasing demand for music also contributed to the emergence of four-part harmony.