Full Idea
If we enquire whether I can consistently universalize the maxim 'I may break my promises only when.....', the gap can be filled by a description devised so that it will apply to my present circumstances, but to very few others.
Gist of Idea
I can universalize a selfish maxim, if it is expressed in a way that only applies to me
Source
comment on Immanuel Kant (Groundwork of the Metaphysic of Morals [1785]) by Alasdair MacIntyre - A Short History of Ethics Ch.14
Book Reference
MacIntyre,Alasdair: 'A Short History of Ethics' [Routledge 1967], p.198
A Reaction
Another good objection to Kant. There is just a huge problem with how you state the maxim under discussion. One man's 'terrorist' is another man's 'freedom fighter'. 'Do everything possible to implement the will of God'.