To nirgrahamUK:
I have various ends, but there is no reason to assume that they are discrete rather than continuous, and no reason to assume that the production function from inputs to achieving ends consists of using one input to achieve one end, and another to achieve another … . Nor is there any reason to assume that the value to you of achieving one end is independent of what other ends you have achieved.
I think that once one takes seriously both how complicated a utility function and how complicated a production function can be, you will discover that if you limit yourself to a priori argument you can’t do much, if any, economics.