来自《耶鲁大学开放课程：金融理论 第8集 第8集》

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  it may be when the bond was issued everybody thought the
  可能因为当时发行的时候人们认为
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  interest rate was going to be 7 percent forever,
  利率将一直是七
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  so that's why they picked a coupon of 7 so that the price
  这是为什么他们把付息定为7
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  when they first issued it would be equal to its face value.
  因此首次发行的价格等于面值
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  But maybe the next day, so it's still a 10-year bond,
  但是下一天 依然是10年期债券
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  practically no time has changed, but unexpectedly the
  其他都没变 但是不像预想的那样
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  interest rates fell to 6 percent.
  利率降到了百分之六
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  If you take the same coupon bond paying 7 all the time at 6
  如果你依然按照7付息
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  percent interest its price is obviously going to go up in the
  而利率为百分之六 价格很定要走高
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  market because everybody is going to discount the 7s,
  因为每个人都能将7折现
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  not at 7 percent, but at 6 percent and get a
  不是按照百分之七 而是百分之六
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  number that's bigger than 100.
  得到的数比100大一点