So we've got a I chord built on the first degree of the scale, a V chord built on the fifth degree of the scale, a IV chord built on the--a IV chord built on the fourth degree, and a VI chord built on the sixth degree.

这样我们就有了建立在第一音级上的I和弦，第五音级上的V和弦，第四音级上的IV和弦，以及第六音级上的VI和弦。

耶鲁公开课 - 聆听音乐课程节选