The error in Aaron's reasoning is that the commutative property is not true for addition. This can be inferred from his claim that adding -5 + 3 or -3 + 5 yields the same result, which is incorrect. In reality, -5 + 3 is equal to -2, while -3 + 5 is equal to 2. The two expressions do not yield the same result. Therefore, the response that best addresses Aaron's error would be:
"The commutative property is not true for addition."