Thomas asked:

In Act-Utilitarianism, how can an agent still act, if the other person has no reason to believe that it's
true, because it might just be said to bring about the best consequences? How can an act-utilitarian
still act according to his belief? And similarly, how can I not desire mere happiness as an end in itself,
but desire things as an end in themselves so that happiness occurs by the way (what Mill suggests in
his autobiography), if I am truly ingrained with the Utilitarian theory? Does not the knowledge of it,
erode it?

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1. In act utilitarianism, the objectively best action is the one that brings about the best consequences,
   measured, e.g. in terms of total happiness. It is irrelevant whether any of the persons affected by the
   action believe in act utilitarianism or not, or agree with the agents calculation of the best
   consequences or not. Furthermore, as Mill makes clear in 'Utilitarianism', when we act on the basis of
   a incorrect calculation of the best consequences, we fail to do the objectively best action, but that
   does not in any way impugn our moral virtue. A good man can, through ignorance, do a bad action.

One curious feature of this theory is that it may be a necessary part of acting so as to bring about the
best consequences, that one succeeds in convincing another person of the falsity of act utilitarianism,
because one knows that they would be likely to make an incorrect calculation. Generally, it seems
quite likely, as Bernard Williams has argued, that the state of affairs with the best consequences for
human happiness is one where the majority of persons never calculate their actions according to the
act utilitarian theory. The act utilitarian can quite easily take this on board.

2. Just as it may be necessary for me to convince another person that they should not calculate their
   actions by the act utilitarian theory, so it seems likely that the best way I can attain happiness for
   myself is to choose projects which I believe will make me most happy, then deliberately 'forget' about
   act utilitarianism and throw myself whole heartedly into those projects.

However, from time to time, I may face prudential or moral dilemmas. When that happens, I will need
to have recourse to act utilitarianism once more.

Geoffrey Klempner