This all leads to a final word of warning. I frequently tell my students that quite a high proportion of what I say is probably wrong, or at least flawed or skewed in some way which I do not at the moment realize. The only problem is that I do not know which bits are wrong; if I did I might do something about it. The analogy with other areas of life is salutary: I make many mistakes in moral and practical matters, so why should I imagine my thinking to be mysteriously exempt? But, whereas if I hurt someone, or take a wrong turn in the road, I am usually confronted quite soon with my error, if
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