Duke University has filed a lawsuit against Aubrey McClendon’s estate to collect a $10 million pledge. In "History of Charitable Pledges," the Wills, Trusts & Estates Prof Blog considers the possible action of a court.
Wealthy people will sometimes make pledges for future donations to a university or charity. This allows the donor to keep assets, yet benefit from the pledge. A challenge can result when that pledge is not fulfilled.
Basically, courts will first look to see if there is an enforceable contract, either bilateral or unilateral. Failing that, the court might try to use a legal doctrine known as “promissory estoppel.” In layman's language that means something like, "You made a promise and the other party relied on it. You received some benefit from your promise, so you should not be able to disavow it."
The bottom line is that the legal system has a public policy preference of seeing that charitable pledges are fulfilled and will seek legal ways they can be enforced.
An estate planning attorney can guide you on donations you intend to make as part of your estate plan.
Reference: Wills, Trusts & Estates Prof Blog (Oct. 9, 2016) "History of Charitable Pledges."