You can be sure of every fact about a gift and still not know what to do. A donation might save a child’s life or protect a forest for a century, and you might know both outcomes exactly while being unsure how to weigh them. That second kind of doubt is moral uncertainty: uncertainty about moral and evaluative questions rather than descriptive ones. In their 2020 book Moral Uncertainty, William MacAskill, Krister Bykvist and Toby Ord argue that, given how hard ethics is and how widely people disagree about it, moral uncertainty is the normal condition rather than the exception.
Ways to decide
Follow your favorite theory. Act on whichever moral view you find most plausible. MacAskill, Bykvist and Ord call this My Favorite Theory and argue that, simple as it is, it has major problems, starting with what to do when you are split between views.
Maximize expected choiceworthiness. Weight each theory’s verdict by how much credence you give it, the way you would weight outcomes by their probability. This works only when theories can be compared on a common scale.
Borrow from voting. Some theories only rank options, and some give amounts that cannot be compared with other theories’ amounts. For those cases the book draws an analogy with social choice, the study of how groups vote, and adapts voting rules such as the Borda rule.
Convene a moral parliament. In 2009 Nick Bostrom proposed imagining that each theory you take seriously sends delegates to a parliament, in proportion to your credence in it. The delegates bargain and vote, and you act on the result. A theory with few seats can still win on the issues it cares about most by giving way on others. Bostrom developed the idea with Toby Ord, and in 2021 Toby Newberry and Ord argued for a version based on proportional chances voting. They also showed that other approaches to moral uncertainty can be read as parliaments with different rules.
Hard cases
The book names two problems any approach must face. Fanaticism is the worry that a theory you barely believe could dominate your choices if it says the stakes are enormous. Infectious incomparability is the worry that giving any credence to a view on which options cannot be compared spreads that incomparability to every decision you make.
In Charitology
Charitology’s answer to the Single Lens is to look at every gift through eight moral frameworks at once: welfare, rights and duties, justice, care, faith and tradition, future generations, all life and flourishing. The Values Compass asks how strongly you agree with a statement from each one, and the Portfolio Builder uses a simple credence-weighted method to turn weights like these into an allocation. Whether more sophisticated methods give different, and more defensible, answers is Open Problem 16.