Able to pay

What does Able to pay mean in American Law?

The definition of Able to pay in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

Upon occasion a person will promise to pay “when able.” This has ordinarily been interpreted as a valid conditional promise (i.e., not the clearly illusory promise that “when willing” would be), and that the promisor need not pay until, by some objective criteria, he is “able” to do so. It is in formulating those criteria of objective ability, and discovering if they are met, that most of the trouble lies, and thus an “able to pay” term can easily lead to expensive, fact-dependent litigation.