In some cases, you can. One apparent problem in SanFran (and I've heard of it in NYC too) is unoccupied properties, which could be used for housing but aren't

In some cases, you can. One apparent problem in SanFran (and I've heard of it in NYC too) is unoccupied properties, which could be used for housing but aren't because their owners prefer to just sit on it and not use it at all (maybe it's a vacation residence or they're speculating its value will rise). If you stick a massive tax on that, that deters that kind of behavior, and forces them to either rent out the property, or sell to someone who will either live in it or rent it out. This will increase the housing supply, which would then decrease the cost of housing overall by providing more supply and more competition. This wouldn't be a tax that people would actually pay, unless they're stupid; they would take steps to avoid paying the tax altogether. Taxes don't make stuff more expensive: they deter behavior. The simple rule is: if you want less of something, tax it. Now, this isn't always true, but to an extent it usually is, especially for consumption. (It's not really true of income taxes usually; everyone usually wants more income, and needs some amount of income, so a tax on that income doesn't discourage that, unless the tax is so high or so wacky that it discourages working for additional income.) Here, we want people to stop leaving properties unoccupied, so we slap a giant tax on that so they'll stop doing it.