What is the difference between marginal utility and diminishing marginal utility?

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pohnpei397 | College Teacher | (Level 3) Distinguished Educator

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Diminishing marginal utility is simply one "kind" of marginal utility.  Marginal utility can be increasing, decreasing, or stable.

Marginal utility is simply the added benefit that a consumer gets from consuming the next unit of some good or service.  In other words, if I have bought and eaten two sandwiches and I buy and eat another, the extra benefit I get from the third sandwich is my marginal utility from consuming the third sandwich.

Diminishing marginal utility comes if I get less marginal utility from consuming the next unit than I got from consuming the previous one.  Using the sandwich example, if I got more marginal utility from the second sandwich than I do from the third (maybe I'm getting too full and didn't really want the whole third sandwich), my marginal utility is declining.

So, there is not really a difference between these two.  It is just that diminishing marginal utility is one "kind" of marginal utility.