Indeed we should
have no justification for protracting our studies if we
were forbidden to improve upon our original views.
Still none of my past teaching was superfluous: for
the views which I am now going to produce will be
found to be based on the same principles, and consequently no one need be sorry to have attended my
lectures, since all that I am now attempting to do is to
collect and rearrange my original views so that they
may be somewhat more instructive. But I wish to
satisfy everybody and not to lay myself open to the
accusation that I have allowed a long time to elapse
between the formation and publication of my views.