Art of War Ch. 5: Jomini Versus Clausewitz — Can War Be Reduced to Rules?

"Jomini gave commanders a map. Clausewitz told them the map dissolves in the rain." — one summary of their disagreement

Military Context

Jomini and Clausewitz were contemporaries who both lived through the Napoleonic wars and reached nearly opposite conclusions about the nature of war. The disagreement has run for two centuries, and it has an exact counterpart in investing.

Jomini's method dominated military academies for nearly a century because it could be taught, examined, and written into doctrine. Clausewitz gradually prevailed during the twentieth century as the complexity of industrial warfare outran what geometric laws could explain.

The Wall Street Translation

1. The Same Argument in Investing

The disagreement reproduces itself completely in investing, with clearly identifiable camps.

Jominian investors hold that markets reduce to rules: quantitative models, technical patterns, factor screens, mechanical systems. Clausewitzian investors hold that markets contain irreducible uncertainty and emphasise judgment, adaptation, and survival.

Books in this library fall on both sides: The Little Book That Still Beats the Market and What Works on Wall Street are Jominian, reducing investing to executable ranking rules. Antifragile and Trading in the Zone are Clausewitzian, insisting uncertainty cannot be eliminated and can only be survived structurally.

2. Which Side Is Right

History's answer is that both are, over different domains.

Rules win where decisions repeat and samples are large — exactly the finding cited in Thinking, Fast and Slow Chapter 1 elsewhere in this library: simple statistical rules consistently beat expert judgment.

Judgment is irreplaceable where samples are thin and rules get arbitraged away — one-off major allocation decisions, structural market change, policy environments without precedent.

3. Where Jomini's Method Specifically Fails

Rules stop working once they are widely known. The military parallel is exact: once your opponent has also read The Art of War, the geometric advantage disappears.

Chapter 5 of What Works on Wall Street elsewhere in this library documents the quantified version: published factors lose a third to half their excess return on average. A rule's effectiveness is proportional to its scarcity.

Actionable Trading Rules

1. Use rules for high-frequency repeated decisions: position sizing, stop placement, rebalancing dates should be mechanical, because consistency beats judgment there.
2. Use judgment for low-frequency major decisions: asset allocation, retirement timing, whether to bear a category of risk — these have thin samples that rules cannot cover.
3. Assume your rules will be arbitraged away: any public rule is in the process of decaying; lower your expected return from it rather than raising your confidence.

Relevance to a Retirement Portfolio

This argument yields a clear conclusion for retirees: apply each method where it belongs.

Use Jominian mechanical rules at the execution layer: automatic contributions, annual rebalancing, a fixed stock/bond ratio. These high-frequency repeated decisions belong to rules precisely because your judgment is unreliable when emotions run.

Use Clausewitzian judgment at the structural layer: how large a cash buffer you need, how much drawdown you can absorb, when to reduce risk. These depend on your particular circumstances and have no universal law.

The most common error is inverting the two: deciding execution details by feel over and over, while handing the major structure of your financial life to some general formula found online.