User talk:Aaquilino

WP:OR

Do not add “original research” to articles on Wikipedia, as you did to “Marginal utility” and to “Marginalism”.

Moreover, while diminishing marginal utility is indeed not a necessary condition for convexity of indifference curves, it is a sufficient condition. McCulloch (in an article cited both at “Marginalism” and at “Marginal utility”) shows this for the general case (where utility is not presumed to have an underlying quantification). —SlamDiego_←T 22:15, 16 October 2008 (UTC)

McConnell

Your reference to McConnell is ill-considered. Nowhere in McConnell is there a proof or even a claim that diminishing marginal utility is insufficient for convexity of indifference curves. (Discussion is in the appendix to Chapter 21.) Again, the claim of insufficiency is “original research”, and it is quite in error. You may need to review the concept of logical sufficiency, and the distinction between this concept and that of logical necessity, before proceeding. —SlamDiego_←T 18:21, 17 October 2008 (UTC)

Not in McConnell's text, but elsewhere, I have found authors claiming that diminishing marginal utility is not sufficient, but this claim is based on a notion of dminishing marginal utility such that is said to be “diminishing” when it is not, in fact, diminsihing. More specifically, it is said to be “diminishing” when it would diminish were it not for interaction with the other good. There is a distinction between utility obeying the “law” of diminishing marginal utility and utility diminsihing more generally. This issue was meant to be picked-up by the “all else being equal” earlier in the articles; I have added a parenthetical notes on complementarity of uses to make matters more explicit. —SlamDiego_←T 10:22, 18 October 2008 (UTC)

The deeper issue is this: marginal utility theorists were aware, before Hicks and Allen, that complementarity could throw a wrench in the works. So they assume(d) an absence of significant complementarity as typical. Hicks and Allen just more baldly assume that indifference curves are convex. In other words, the marginal utility theorists assumed-away one thing which would lead to non-convex indifference curves, while Hicks and Allen just assumed-away the non-convexity. The fact that marginal utility theory needs the one assumption, whereas Hicks and Allen make the other, doesn't show that the former is somehow incorrect or that the latter is somehow more advanced. —SlamDiego_←T 22:20, 18 October 2008 (UTC)