Over time, the value of a house increases but its mortgage decreases. Which of the factors is independent?

The value of a house and the mortgage amount are both dependent on time. Over time, the value of a house generally increases due to factors such as market conditions, improvements made to the property, and inflation. On the other hand, the mortgage amount decreases over time as the homeowner makes regular mortgage payments, reducing the outstanding loan balance.
Therefore, the factor that remains constant and independent in this situation is time, as it continuously progresses while the value of the house increases and the mortgage decreases.