Wake Forest University

Traditional:

63
　　春為感，夏為應；秋為感，冬為應。若統論，春夏為 感，秋冬為應；明歲春夏又為感。可學。四時。
Translation:
Spring is (emotional movement =) a stimulus, and summer is its response. Autumn is (emotional movement =) a stimulus, and winter is its response. If a (comprehensive =) broader scaoe account be made, then spring and summer are (emotional movement =) the stimulus, and autumn and winter are its response. In the following year, spring and summer are again the stimulus, and summer and autumn are again its response. Ke Xue, Si Shi
Commentary:
Zhu Xi appears to be saying that what happens in spring sets off, somehow, what happens in summer. Then there appears to be a lack of causal connection, because he next mentions the fall and winter pair without saying how fall comes to follow summer. He takes care of this problem by embedding the two sequences in a larger sequence. He says that spring-summer acts as a stimulus for autumn-winter. But he does not explain what touches off the appearance of spring or spring-summer in the next year.
This rather odd schema is actually very characteristic of the basic Chinese paradigm for explaining cyclical change, and perhaps all change. Beyond the level of the Tai-ji, everything is explained in terms of cycles that contain cycles within themselves. The easiest way to think of this is to recall that the string of an instrument such as the violin moves in a fundamental vibration which begins with the center of the string being moved to the left or right and then snapping to the other extreme when the string is released. But each half of the string will also soon begin to vibrate at a frequency double that of the whole string, and so forth. So the movement of the first quarter length of the string to the left would correspond to spring, the movement of the second quarter of the string to the right as the whole string moved to the right would be summer, the movement of the third quarter of the string to the right as the whole string moved to the left would be autumn, and the movement of the fourth quarter to the left as the whole string moved to the left would be winter. When the second quarter is moving to the right as the whole string is moving to the right, it gets farther to the right than any other part of the string. When the fourth quarter is moving to the left as the whole string is moving to the left, it gets farther to the left than any other part of the string. The only trouble with this analogy (which also seems to characterize Zhu Xi's thinking on these subjects) is that all of these motions are going on at the same time, whereas the seasons occur successively in time.