Dear list members, I would be very interested in your opinion in the following matter. One = frequently reads in econometric papers that certain economic variables = (e.g. inflation, GDP, unemployment) are termed "observable" while others = (e.g. the NAIRU, potential output, the causal effect of some x on some = y) are called "unobservable". I have two questions about this: 1) What do you think is the explanation for this difference/distinction? Please be as specific as possible (e.g. if you think it is a matter of = direct vs indirect measurability, say exactly what that means; similarly = if you think it's a matter of measurable vs estimable etc. etc.). 2) What are the loci classici for discussions of the concept of = observable IN ECONOMICS? Again, please be as specific as possible: I am NOT looking at = testability, verfifiability, falsifiability etc. but observability. One = place is certainly Oskar Morgenstern's On the Accuracy of Economic = Observations. Uskali Maki sometimes talks about observables but I think = he uses a different concept (according to which variables such as = inflation would UNobservable). Many thanks! Julian Reiss