Descriptive and prescriptive theses
A descriptive thesis makes a claim about how things are. A prescriptive thesis makes a claim about how things should be. (Think of a doctors prescription, which tells you what you should do to get well, as opposed to a diagnosis, which simply describes your illness.) You can agree with someone about how things are even if you dont share their values. But you cant agree on how things should be unless you share at least one value. Therefore, prescriptive theses deal with questions of values, ethics or morality.
Here are some features of each type of thesis.
A descriptive thesis
- makes an is statement
- appeals to evidence that anyone (given enough training) can observe and confirm
- appeals to logic that anyone (again, given enough training) can test and confirm
- deals in measurement, analysis, interpretation, explanation
A prescriptive thesis also uses evidence, logic, measurement, analysis, interpretation and explanation. However, unlike a descriptive thesis, it also
- makes a should statement
- appeals to shared values or moralsassessments of what is good and bad or right and wrong.
Some examples of descriptive theses (notice that disagreement on these points is possible, even though they make
factual or analytical claims):
- Racism in this country has historical roots in taking land from and destroying indigenous peoples and enslaving Africans to work that land (Loewen, 143).
- Global warming is caused by human activity, not natural changes in the climate.
- American popular music is rooted in the folk tradition of African Americans.
- The United States does not offer equal economic opportunity to all of its citizens.
Some examples of prescriptive theses:
- We all need to work hard to overcome the legacy of slavery and racism.
- Global warming must be stopped!
- Music teachers should teach the African American roots of American popular music.
- Everyone deserves equal economic opportunity.
In some cases a descriptive thesis may strongly imply a prescriptive argument as well (as in most of the examples above). However, note that one can agree or disagree with the descriptive thesis regardless of how one feels about the moral question. For example, you might agree that global warming is real and caused by human activity, but may not believe it is a bad thing.
Loewen, James. Lies My Teacher Told Me: Everything Your American History Textbook Got Wrong. New York: Touchstone, 1996.