Editing Utilitarianism (section)

===Calculating utility is self-defeating===
An early criticism, which was addressed by Mill, is that if time is taken to calculate the best course of action it is likely that the opportunity to take the best course of action will already have passed. Mill responded that there had been ample time to calculate the likely effects:<ref name="Mill, John Stuart">{{cite web |url=http://www.utilitarianism.com/mill2.htm |title=Utilitarianism, Chapter 2 |author=Mill, John Stuart |access-date=24 June 2012}}</ref>
{{blockquote|[N]amely, the whole past duration of the human species. During all that time, mankind have been learning by experience the tendencies of actions; on which experience all the prudence, as well as all the morality of life, are dependent...It is a strange notion that the acknowledgment of a first principle is inconsistent with the admission of secondary ones. To inform a traveller respecting the place of his ultimate destination, is not to forbid the use of landmarks and direction-posts on the way. The proposition that happiness is the end and aim of morality, does not mean that no road ought to be laid down to that goal, or that persons going thither should not be advised to take one direction rather than another. Men really ought to leave off talking a kind of nonsense on this subject, which they would neither talk nor listen to on other matters of practical concernment.|author=|title=|source=}}

More recently, Hardin has made the same point. "It should embarrass philosophers that they have ever taken this objection seriously. Parallel considerations in other realms are dismissed with eminently good sense. Lord Devlin notes, 'if the reasonable man "[[work-to-rule|worked to rule]]" by perusing to the point of comprehension every form he was handed, the commercial and administrative life of the country would creep to a standstill.{{'"}}<ref name="Hardin 1990 4">{{cite book |last=Hardin |first=Russell |title=Morality within the Limits of Reason |publisher=University of Chicago Press |date=May 1990 |page=4 |isbn=978-0-226-31620-8}}</ref>

It is such considerations that lead even act utilitarians to rely on "rules of thumb", as [[J. J. C. Smart|Smart]] (1973) has called them.<ref>{{cite book|last1=Smart|first1=J. J. C.|url=https://archive.org/details/utilitarianismfo00smar|title=Utilitarianism: For and Against|last2=Williams|first2=Bernard|date=January 1973|publisher=Cambridge University Press|isbn=978-0-521-09822-9|pages=[https://archive.org/details/utilitarianismfo00smar/page/42 42]|url-access=registration}}</ref>