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A person is obligated to pay for the damage that he causes. The conventional method of evaluating the amount of damage is by calculating the difference between the item's resale value before and after the damage. However, this approach is difficult to apply to many casses. For example, how much must a mazik pay for breaking a window of a house or cracking the bumper of a car? According to the traditional approach, the mazik should pay the resulting depreciation of the resale value of the house or car. The obvious problem is that although it costs hundreds of dollars to replace a window, the real-estate value of the house usually does not depreciate because of a minor damage. Likewise, if a bumper is slightly cracked, the depreciation of the car's resale value may be minimal. Nonetheless, the only way to fix the damage is to replace the entire bumper which will cost hundreds of dollars. How does halacha approach such scenarios- is it sufficient for the mazik to pay for the depreciation, or must he pay the larger sum needed to make repairs?

The Raavad writes (Toe'in 5,2), "if a person damaged his friend's field by digging furrows in it, the owner can require him to fill them". Apparently, the Raavad views the obligation of the mazik as more than just to pay for the damage, but even to physically restore the item. The Magid Mishnah finds it difficult to compel the mazik to manually fill the ditches instead of just paying for the loss. The Shach (CM 95:18,387:1), however, rules that part of the mazik's obligation is to actually fix the damage, if the owner wants him to. The Chazon Ish (Bava Kama 6) offers a different interpretation of the Raavad's comment. He understands that the Raavad did not mean that the mazik must actually fill the furrows. Rather, the fundamental obligation of the mazik is to restore the field to its original state. Therefore, it is not sufficient to simply pay for the field's depreciation. Instead, the mazik must pay the cost of hiring workers to restore the field, which may be significantly higher than the depreciation in value.  

The Chazon Ish extends this analysis to damage inflicted on a single wall of a house. He writes that since owners do not dispose of houses because of such damage, but simply repair the wall, damages cannot be evaluated based on the depreciation of the house's market value. Rather, the true value of the damage is the cost of the repairs. In the same vein, one who broke a window of a house must pay the cost of installing a new window.

The approach of the Chazon Ish also applies to evaluating damages to cars. Determining damages based upon resale value is only sufficient if an owner would typically  sell the car and not fix the damage. However, if it is the norm to fix the car, then the owner has a right to ask for the amount the repairs will cost. Therefore, if the entire bumper must be replaced in order to fix a crack, he is obligated to pay the cost of replacing the bumper.

In Yeshivos, our issue is discussed with respect to the underlying logic behind paying for damages. Is monetary compensation the fundamental responsibility of the mazik? Or perhaps, the fundamental responsibility is to restore the item, and paying the value is just in lieu of the repairs. The classical difference between these approaches is if the cost of replacing the item changes after the time of the damage. For example, if at the time of the damage it would cost $50 to repair the item, but now at the time of payment the item can be replaced for $40. If monetary compensation is the essence of the mazik's obligation, then at the time of the damage the mazik became obligated to pay $50, and that would not change regardless of whether the cost of repair subsequently changes. However, if the essence of the obligation is to replace the item, and a comparable item can now be bought for $40, that is sufficient to fulfill his obligation. The Machaneh Efrayim (Nizkai Mamon 1) understands that according to many Rishonim it is sufficient to pay the lower amount.  The Chazon Ish points out, according to the Shach who obligates the mazik to actually repair the damage, it would seem that only the present cost of replacement is relevant. This is because the money is only being paid in lieu of the mazik actually fixing the item, and the value at the time of damage is unimportant. Therefore, whether the object was worth $50 but now can be bought for $40, or if it was worth $40 at the time of the damage but now can only be purchased for $50, we always follow the time of payment.