Qualitative economics
Qualitative economics is the representation and analysis of information about the direction of change (+, -, or 0) in some economic variable(s) as related to change of some other economic variable(s). For the non-zero case, what makes the change "qualitative" is that its direction but not its magnitude is specified. Typical exercises of qualitative economics include comparative-static changes studied in microeconomics or macroeconomics and comparative equilibrium-growth states in a macroeconomic growth model. A simple example illustrating qualitative change is from macroeconomics. Let: Monetary theory hypothesizes a positive relationship between "GDP" the dependent variable and "M" the  independent variable. Equivalent ways to represent such a qualitative relationship between them are as a signed functional relationship and as a signed derivative: where the '+' indexes a positive relationship of "GDP" to "M", that is, as "M" increases, "GDP" increases as a result. Another model of GDP hypothesizes that "GDP" has a negative relationship to "T". This can be represented similarly to the above, with a theoretically appropriate sign change as indicated: That is, as "T" increases, "GDP" decreases as a result. A combined model uses both "M" and "T" as independent variables. The hypothesized relationships can be equivalently  represented as signed functional relationships and signed partial derivatives (suitable for more than one independent variable): Qualitative hypotheses occur in earliest history of formal economics but only as to formal economic models from the late 1930s with Hicks's model of general equilibrium in a competitive economy. A classic exposition of qualitative economics is Samuelson, 1947. There Samuelson identifies qualitative restrictions and the hypotheses of maximization and stability of equilibrium as the three fundamental sources of "meaningful" theorems — hypotheses about empirical data that could conceivably be refuted by empirical data.