> We hold the demand curve constant for any such analysis. And this is the portion that I'm critiquing. You're holding it as a constant curve sloping downwards

> We hold the demand curve constant for any such analysis. And this is the portion that I'm critiquing. You're holding it as a constant curve sloping downwards. > So yes, we do have an idea of some fundamental properties of the demand curve Okay, sure, it relies on there being people who have demand for some commodity. > it cannot simply be any polynomial "Any polynomial" might be overselling it, but we can't assume it's sloping downwards.