The effect of the use of descriptive language can depend on evaluative considerations. For philosophy of law, that dependence raises special problems. If you cannot tell whether to describe an object as a ‘vehicle’ for the purposes of the Act without evaluative reasoning, then the legal effect of the Road Traffic Act does not depend merely on physical facts (such as that there were wheels on the chicken coop) and social facts (such as that Parliament used the word ‘vehicle’ in the Act, or the co