How Paul Krugman gets away with saying stuff he knows is unsupported by theory: suggest that a core economics concept is a "common-sense notion" and quickly then move on to discuss its implications in policy...
nytimes.com/2019/01/05/opi…
nytimes.com/2019/01/05/opi…
He of course knows well that diminishing marginal utility is a core understanding in marginal economics, which has been core to the field since the early 1870s. And he also knows that inter-personal value comparisons are illegitimate (if not impossible) under the understanding
of value as subjective (also a core concept). So one cannot, with economic theory, say what he's saying. But by claiming it is a "common-sense notion" using one illustration that seems intuitive, he manages to lie without telling a lie: his use of a technical term that everybody
knows is used in economics, and even sounds like economics (and is used by a known economist too!), his conclusion is given an air of legitimacy even though he really uses the term as "common-sense" and not theoretically. So he can then move on to discuss his conclusion, which
actually does *not* follow from the economic theory, with the reader lured into thinking (with the author's help) that Krugman's argument is supported by theory. But it is not. Diminishing marginal utility does not support his high-tax argument in this way, which Krugman surely
knows. It only supports that argument if used in a common-sense sense, by which is meant: with a meaning without theoretic precision and, in fact, in a sense that is not even theoretically supported. In other words, when used in a way that is simply no longer economic theory.
