Prerequisites
Comparative history, causal arguments, source dependence, and counterfactual reasoning.
A before-after sequence is consistent with many mechanisms. State rival explanations and seek evidence that distinguishes them. Comparison cases help only when their differences and record-making processes are examined, not assumed away.
Worked example
If two ports adopt a reform but only one expands trade, the contrast challenges a simple sufficient-cause claim. It does not by itself identify which other factor mattered or prove the reform had no effect.
Model and Assumptions
Fictional comparison: Port A introduced a fee reform in 1880 and rail access in 1881; recorded cargo rose in 1882. Port B introduced the same nominal reform in 1880 without rail access; its recorded cargo stayed flat. A also changed its cargo-recording rules in 1882.
Further inquiry
Build a table of predictions under fee, rail, and recording-change explanations. Identify one observation that could weaken each. Write a qualified counterfactual claim and explain why the comparison cannot identify a numerical causal effect on its own.
Review criteria
- Tie each proposed source to a discriminating prediction.
- Examine both implementation and measurement comparability.
- Avoid treating chronology or one comparison as a complete causal design.