Part of the Ice and Dilution school. Class 3 of 6.
The capability: you choose the technique from the ingredients and you can defend the choice.
Prerequisites: Modules 10, 40.
The practice
Make the same spirit-only drink shaken and stirred. Look at both. Taste both.
Then the same citrus drink both ways.
Then a sour at three shake durations, finding where the tin frost and the correct dilution actually line up.
Then fine-strain half a shaken drink and not the other half, and taste both at three minutes — because ice fragments keep diluting after service and in this room the table is a hundred feet away.
The reference
The four drinks from the first two exercises, which demonstrate the rule rather than assert it.
What you are building
The rule as an observation rather than as a tradition.
Citrus, dairy, egg, or purée means shake. Otherwise stir, per Module 40 — and the reason is mechanical: those ingredients benefit from aeration, and a spirit-and-modifier drink has nothing to gain and clarity, density, and fragment-free dilution to lose.
Verification and boundary
Blind: two versions of the same drink, identify which was shaken.
Boundary: raw egg service requires the venue's consumer advisory and the local health authority governs.