What does the Phillips curve illustrate when inflation increases?

The Phillips curve illustrates the inverse relationship between inflation and unemployment in an economy. Specifically, when inflation increases, the Phillips curve suggests that there is typically a corresponding decrease in unemployment. This relationship can be understood through the short-run trade-off: as prices rise, businesses may respond by increasing production to capitalize on higher consumer demand, which often leads to hiring more employees. This increase in demand for labor typically results in lower unemployment rates.

Furthermore, expectations also play a role in this relationship. In the short run, if inflation expectations remain stable, an increase in inflation can incentivize firms to expand operations, thereby reducing unemployment. However, it's important to note that this trade-off may not hold in the long term, as adaptive expectations about inflation can shift the curve.

The other options do not directly align with the implications of the Phillips curve when inflation rises. Investment, on one hand, could potentially rise, but it's not a direct outcome illustrated by the Phillips curve. An increase in inflation does not inherently lead to a decrease in inflation or guarantee an increase in wages across the board, as these dynamics depend on various economic conditions and labor market responses. Thus, the most accurate representation of the Phillips curve when inflation increases is the decrease in unemployment.