数学史家Morris Kline在Mathematicsand the Physical World里引用了中世纪哲学家Roger Bacon的一段话，恰好可以用来作为我的数理方法课的引子:

  Mathematics is the gate and key of thesciences. . . . Neglect of mathematics works injury to all knowledge, since he who is ignorant of it cannot know the other sciences or the things of this world. And what is worse, men who are thus ignorant are unable to perceive their own ignorance and so donot seek a remedy. -

最后一句特别好：更悲剧的是，对数学无知的人感觉不到自己的无知。遗憾的是，700多年前的人就意识到了的问题，今天似乎更加严峻了。

又看见有人概括大自然的两点“艺术风格”：对称（symmetry）和简约（economy）。前者表现了对和谐、均衡和比例的钟爱，后者则醉心于从有限的方法得到丰硕的结果。这样的风格，当然也是数学的风格。