>For the special case of dollars, it makes sense that there's no "capital gain" to tax: since the "capital gain" is measured in dollars, the gain or loss on you

>For the special case of dollars, it makes sense that there's no "capital gain" to tax: since the "capital gain" is measured in dollars, the gain or loss on your dollars is always zero. Unless you sell your very rare, misprinted 100 dollar bill for $100k? You definitely owe tax on that payment but I have no clue which part of tax law that falls under, and I'm pretty sure I don't understand what a "capital gain" is.