 Among the views of moral realists, differences in content are less significant than similarities. For all such philosophers, morality prohibits actions such as killing, causing pain, deceiving, and breaking promises. For some, morality also requires charitable actions, but failure to act charitably on every possible occasion does not require justification in the same way that any act of killing, causing pain, deceiving, and breaking promises requires justification. Both Kant (1785) and Mill (1861) distinguish between duties of perfect obligation and duties of imperfect obligation and regard not harming as the former kind of duty and helping as the latter kind of duty. For Gert (2005), morality encourages charitable action, but does not require it; it is always morally good to be charitable, but it is not immoral not to be charitable.