> In English, "buy the textbook only if you can afford it" means the same as "affording the textbook is necessary to buy it". That is a tautology; that's true f

> In English, "buy the textbook only if you can afford it" means the same as "affording the textbook is necessary to buy it". That is a tautology; that's true for literally everything: to buy something, you need to afford it. Having the ability to throw the money around is not the same thing as being able to afford to spend that money. Americans are very credit-happy, among other things. Or imagine it says something more like "don't give us money if that would cause you to be unable to make rent/afford food/hoard candles".