That definition works for things like gold bricks or stocks that are purely treated as assets, but it can create some odd outcomes.

In the 90s there were stories of a fan who caught a milestone home-run baseball and because of its sentimental value didn't want to sell it, but had to do so in order to pay the tax bill.

In the extreme case, if I have a child, does that constitute income equal to the price a human-trafficker would be willing to pay for him or her?