The TLRC Committee has been considering the relationship between tax and accounting measures of business income. This paper builds on the earlier discussion paper DP2 issued in April 2002, which set out some of the general issues of principle involved in any such alignment. The government is clearly attracted to aligning the corporate tax system more closely with account, and significant legislative advances in this direction have already been achieved. As a general matter this is to be welcomed, for reasons which are examined in this paper. But an examination of the principles involved leads us to conclude that now is the time to reflect on where the limits to alignment might lie. It is with this question in mind that Graeme Macdonald and Martin have written this paper at the request of the Committee as a response to the August 2003 consultation document, Corporation Tax Reform.