Keeping alternate history anchored to evidence

How can a professional historian approach alternate-history questions responsibly?

Start with a tightly defined question, state what cannot be predicted, and use the counterfactual to examine historical constraints rather than inventing an unlimited future.

Alternate history can improve understanding of actual events by examining roads not taken. A tightly defined question limits how far the analysis can run. Peacetime developments within one navy are easier to assess than a succession of second-, third-, fourth- and fifth-order consequences. Predictions need explicit limits and honesty about what cannot be established. Beyond those limits, the exercise becomes imaginative fiction.