Full Idea
As to what activities we ought to engage in, what ends we should pursue, the categorical imperative seems to be silent.
Gist of Idea
The categorical imperative says nothing about what our activities and ends should be
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.197
A Reaction
I think this is the fatal objection to Kant's view. He says, for example, that promise-breaking is inconsistent with a belief that promises are good, but who said promises are good? No ethical system can get started without values.