How the (Econometric) Sausage is Made

Admittedly, I don't always English so good. However, usage of the terms "internal validity" and "external validity" in the causal inference literature has baffled me a bit. So, I did some investigating. We all know what these terms mean. So much so they typically don't merit more than a passing definition. But, I think these terms do require a bit more thought in one aspect. All of us ensconced in the causal inference world presumably have heard, been taught, or even repeated the mantra: "Randomized Control Trials (RCTs) have greater internal validity, but observational studies have greater external validity." Is this really true? It depends on how we define internal and external validity. To my knowledge (h/t Manski), the distinction between the two concepts dates back to Campbell & Stanley (1963, p. 5) who write: "Fundamental to this listing is a distinction between internal validity and external validity . In