We have seen that with just a basic understanding of supply and demand, we can make reasonably accurate qualitative predictions about expected changes in market price and/or quantity. We can also give likely explanations for observed changes in equilibrium price and quantity in terms of likely changes in demand and/or supply.

Without more information, we can't make quantitative predictions. That is, we can't predict the equilibrium price or quantity, only the likely direction of change. However, such qualitative predictions are often good enough and can provide very powerful insights into the workings of markets, and the likely impacts of changes in factors that affect demand or supply.

When we have mathematical demand and supply relationships, we can determine equilibrium price and quantity exactly when demand or supply, or both shift. The same is true, usually, if we have tabular data.

In reality, we often don't have reliable mathematical statements or completely reliable tabular data for demand and supply so we typically have to rely on the kinds of qualitative predictions that are afforded by our standard graphical analysis.