 Practical reasons are practical only if they could be brought to bear on some decision resulting in action; being an action is a status (the generic move) within Intendo; so there could be no practical reasons coming from outside the practice of Intendo. (Other, more local practices have to accommodate reasons that come from outside the practice; for instance, in chess, the object of the game is to win, but I may have personal reasons for not playing to win.) Therefore, if you can show that Intendo imposes some standard on its reasons (for instance, and to anticipate, that they have to be universalizable), then you will have shown that all reasons have to meet it.