We assume that causes contribute to their effects through continuous processes, generally involving intermediate steps. Such processes may be represented by boxes-and-arrows diagrams which express simple ‘theories of change’. We illustrate this using examples from Barbados’s sugar-sweetened beverages tax. The formal relations outlined in Chapter 1 dictate that causation cannot be cyclical. So graphs with cycles needn’t be inconsistent – they just need to be unwound with careful temporal labels to distinguish each time ‘the same’ feature occurs. Developing theories of change often involves starting with relatively simple ones, then testing and refining their contents..