Reasoning with Prescriptive Claims
Descriptive claims say how the world is, was, or will be. Prescriptive claims say how the world should be. We have fairly clear rules for reasoning with descriptive claims. The goal of this essay is to clarify how to reason with prescriptive claims.
Truth and Reasoning
A major goal of reasoning is to establish truths and to determine what would follow if certain assumptions are true. There are many different notions of what is true, both in what kinds of things are true or false and what makes them true or false. By looking at what is common to those we can find an idea of truth and the things that are true that can accommodate many particular views of truth and account for the wide agreement on what counts as good reasoning.
What is the difference between descriptive theories and prescriptive theories? Unless we assume that prescriptive theories are about value-judgments that are not true or false, and hence adopt a new methods and justification for our reasoning, there seems to be no difference that would affect how we construct and evaluate theories.
Except for a clear minimal notion of rationality the use of that term is too vague to be helpful and can be replaced with other common terms that are clearer. Generally, the ascription of rationality or irrationality is a value judgment and not a tool of analysis.