There are other rabbinically forbidden types of interest. Mishnah says: If somebody gives a loan to his friend, he shouldn't go live in the borrower's courtyard for free without paying rent. And he's not allowed to rent from him for less than the normal going rate. This is a rabbinic type of forbidden interest. If a person allows the lender to live in the house for free or for less than the going rate, it's a gift to the lender. So it looks like he's paying him back, and he's also giving him the ability to live in that house for free. So that gift, quote unquote, is a type of interest.
Now we'll talk about a new type of forbidden interest: charging a higher price for a sale or rent that's paid later on, as opposed to asking for the money right away with the discounted price. Mishnah says: You're allowed to increase the amount of rent that you're charging someone who's not paying you the rent in advance. But you're not allowed to increase the price a person is going to pay for a sale. A buyer who's not going to pay up front will explain. Ketzad, what are we talking about? A man rents his courtyard to another person and tells him, “If you give me the rent for the entire year right now, I'll charge you 10 sela (a monetary unit) for the whole year. But if you want to pay me month by month, I'm going to charge you one sela per month,” which equals 12 sela for the year. We say Mutar. It's allowed. It's permitted. The rent is really due at the end of the month, and therefore the true price of the courtyard that he's renting is 12 sela. What the landlord here is deciding to do is tell him, “If you give me the money in advance, I'm going to discount you two of those sela,” as opposed to saying the real price is 10 and he's owed the money in advance. If he doesn't want to pay it, he's going to charge him an interest fee of two sela. That's not how it's looked at. The starting point is 12 sela, which is the amount of one sela per month. If he pays it early, he'll give him a discount. So therefore, in that case, it's allowed. It's Mutar.
But in the other case, if he's selling his field to another person, let's say he tells him, “If you're giving me the money for the field right now, the field will only cost you 1,000 zuz (a coin). But if you want to delay paying me until later on, until the time of the threshing, when the grain is going to be ready and you can take that grain to the marketplace and sell it and raise more money to pay me, then the price for this property is going to cost you 1,200 maneh (a monetary unit).” In this case, it's asur (it would be prohibited). The field was sold originally, and therefore payment is due right away. That payment is 1,000 zuz, and that's what should be paid to him. When he tells him, “If you don't pay me until later on, it's going to cost you 1,200 zuz,” that's considered to be a charge. That's a charge of interest for the waiting period, and therefore that is a forbidden type of interest on the part of the seller of this property. So for rent, it would be allowed. But here, for the buying or selling of this property, it would be prohibited.