Descriptive versus Proscriptive Questions#

In our previous readings, we introduced three classes of questions: Exploratory, Passive-Predictive, and Casual. But that was actually a slight simplification… (sorry).

Above this three-fold distinction in question types, there’s actually a higher-level way to classify questions: Descriptive questions and Proscriptive questions. Descriptive questions are questions that aim to describe something about objective reality, such as “what is the current tax rate for people earning over 250,000 dollars?” or “in what US states is marijuana legal?”.1 Exploratory, Passive-Predictive, and Casual questions are all examples of descriptive questions. Proscriptive questions, by contrast, are questions about how the world should be, like “should the current tax rate for people earning over 250,000 dollars be higher?” or “should marijuana be legal?.

The reason we’ve chosen to focus on descriptive questions rather than proscriptive question is that while data science is an amazing tool for telling us about the state of the world, it cannot, on its own, answer should questions. That is because answering should questions requires evaluating the desirability of different possible outcomes, and that can only be done using on the basis of a system of values. Data science may tell us the consequences of different courses of action, but it cannot tell us whether those consequences make a given course of action worthwhile.

To illustrate, suppose you are interested in reducing opioid overdoses. Your rigorous data science analysis may tell you that increasing the regulation of opioid prescriptions will reduce overdoses by some amount X and reduce access to opioids for those with chronic pain by some amount Y. But does that mean you should enact the policy? Well, that depends on how much value you place on patients with chronic pain having access to opioids, and how much value you place on preventing overdoses. And the answers to those questions simply can’t come from your data.

In this course, we will refer to questions about how the world is as “descriptive questions”, and questions about how the world should be as proscriptive questions. But be aware these terms aren’t universal. Some people (e.g. social scientists) prefer the terms “positive” instead of descriptive and “normative” instead of proscriptive. But the meaning is the same.


Yes, we are positing an objective reality, which admittedly is an idea which has its own complications. However, if you are familiar with the epistemological issues around the idea of an “objective reality” I suspect you are already familiar with the distinction being drawn in this section.