Hello João Batista Ferreira. I think I understand where you are coming from.

The confusion you're experiencing regarding the axes on the demand curve is quite common and stems from the traditional way economists present this relationship. Typically, in most graphs, the independent variable is placed on the x-axis and the dependent variable on the y-axis. However, the demand curve in economics is an exception to this rule. The demand curve is a graphical representation of the relationship between the price of a good or service and the quantity demanded by consumers. While it might seem logical to think of price as the independent variable, economists often treat price as the dependent variable for several reasons.

Firstly, the tradition of plotting price on the y-axis and quantity on the x-axis dates back to early economic theories and has been maintained for consistency and ease of communication within the field. Secondly, the demand curve illustrates how much of a product consumers are willing to purchase at various price points. In this context, the quantity demanded is often viewed as responding to changes in price, which makes quantity the dependent variable. Lastly, economists are often interested in how much consumers will buy at different prices, rather than how prices change with varying quantities. This perspective focuses on consumer behavior and decision-making.

Consider a simple example of a demand curve for coffee. Suppose at a price of $5 per cup, consumers are willing to buy 100 cups per day. If the price drops to $3, the quantity demanded might increase to 150 cups per day. On a graph, you would plot these points with price on the y-axis and quantity on the x-axis. The demand curve would slope downward from left to right, reflecting the inverse relationship between price and quantity demanded: as price decreases, quantity demanded increases. While the traditional economic presentation places price on the y-axis, it's important to note that in some analyses, especially in econometrics or specific economic models, researchers might choose to invert this relationship to focus on how price changes in response to varying quantities. This approach can be useful in supply-side analysis or when examining price elasticity. While it might seem counterintuitive based on typical graphing conventions, the placement of price and quantity on the demand curve is rooted in historical economic practice and focuses on understanding consumer behavior. The key takeaway is that the demand curve illustrates the inverse relationship between price and quantity demanded, regardless of which variable is on which axis.

João Batista Ferreira You're correct that traditionally in many graphs, the independent variable is placed on the X-axis and the dependent variable on the Y-axis. However, in the context of economics, the demand curve is usually represented with quantity on the X-axis and price on the Y-axis, even though it might seem counterintuitive given the standard convention.

Why This Representation?

What If We Switched Axes?

If you were to switch the axes—putting price on the X-axis and quantity on the Y-axis—you'd still have a valid representation of the relationship between price and quantity. However, it would no longer follow the conventional depiction used in economic analysis, and could potentially cause confusion when communicating with others who are accustomed to the standard format.