 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 complex social fact of the whole pattern of uses that have been made of the word ‘vehicle’). You cannot identify the law (that is, you cannot tell what legal rights and duties people have) without evaluative reasoning. That conclusion, if it is sound, seems to have important implications for the long-running debates in theory of law over the relation between fact and value in law, and over relations between law and morality. The conclusion seems to contradict one of the most provocative and controversial claims in the theory of law—the ‘sources thesis’, which Joseph Raz has stated as follows: