Here's why:
* Common noun: When "curse" refers to a specific, concrete instance of a curse, it's a common noun. For example: "The witch put a curse on the village." Here, "curse" refers to a specific supernatural event.
* Abstract noun: When "curse" refers to the general concept of a curse, it's an abstract noun. For example: "She believed in the power of curses." Here, "curse" represents a broader idea or concept.
So, the classification of "curse" depends on the context.