Robert Leeson's point is correct if the issue is what is the best way to conceptualize aggregate demand. This hyperbolic formulation is clearly a curious theoretical construct that one would never observe in the real world if one could see AS shifting without AD shifting, and for the reasons he states. Personally, I prefer AD curves whose downward slope is justified on such boring grounds as international substitution effects, wealth ("Pigou") effects, and interest rate ("Keynes") effects. But some on this list have been busy declaring that AD is simply a useless concept for various reasons, with this long proven and accepted by everybody and anybody who has a grain of sense or knowledge of what has been going on in economics. Barkley Rosser