They're these building blocks that support the melody and they have to change for that melody to be consonant all the time.

这些和弦是旋律的基础,和弦的变化必须和旋律保持协调一致

耶鲁公开课 - 聆听音乐课程节选

The sum of path number 2 and path number 3 get me to the same place, so the energy change by going through this time path, this intermediate point here back all the way to final state should be the same the red path.

而经过路径2和3可以3,到达同样的末态，因此经过路径,2和3带来的能量的变化，与路径1带来的,能量变化相同。

麻省理工公开课 - 热力学与动力学课程节选