The marginal utility is, in plain English, the additional benefit (utility) that an individual gets by consuming an additional unit of a good or service. According to the Law of Diminishing Marginal Utility, the utility of an additional unit of a good is inversely related to the number of units consumed already. In turn, the marginal productivity (or marginal product) is the production gain got by a given plant when a given input is increased by one unit. It is often argued - with some reason, I must add - that the productivity gain got by applying extra input units will increase only marginally from one unit to the next, which is known as the Law of Diminishing Marginal Productivity.
I am not an Economist but, for me, it is clear that both Marginal Utility and Marginal Product are one and the same concept. Indeed, the former is derived from a demand perspective and the latter from a supply perspective. See, if you write down the phrase "the additional X got when an additional unit of Y is consumed" and replace "X" by "utility" and "Y" by "a good or service", you have defined "marginal utility". Similarly, if you change "X" and "Y" by "productivity" and "an input", this phrase becomes a decent definition of marginal productivity. Judging by the graphs I've seen here and there, even the underlying mathematical models that describes both concepts look indistinguishible.
Is that impression correct? Are marginal utility and marginal productivity two different perspectives of the same concept? Does that make any sense?