This note is based on our collective experiences in working with organizations to develop their theory of change. One of the most eye-­opening aspects of the work for participants – and us – is that of identifying assumptions. Suddenly having an ‘aha’ moment about a long held and problematic assumption has been powerful, helping to: understand what works and why/or understand why things did not work, generate new strategies and actions, pinpoint information for outcome or impact reporting, and reveal why organisations in a partnership might not be working well together… yes, their assumptions differ.

We consider thoughtful assumption identification an essential aspect of a ToC process. Yet it is often poorly done. Common problems with assumptions are that people identify too few or too many, fail to see critical assumptions, and focus only on context assumptions while ignoring causal assumptions. We hope these notes can give ideas on how to improve this vital aspect of any good ToC process. After defining assumptions, this note explains their utility and gives some ideas about how to work with them effectively.