 It is true that, in order to decide what the sources have directed (and thereby, in Raz’s terms, to identify the existence and content of a law), you need to understand the sense in which a word like ‘vehicle’ is used. But the existence and content of the offence can still be identified without first judging whether it ought to be an offence to do what Mr.Burr did, or whether there ought to be any offence at all of driving without pneumatic tires. The sources thesis articulates this important insight: in English law, there was no offence of driving without pneumatic tires (whether or not it would be a good idea for that to be an offence), until Parliament acted to create the offence. And then, it became an offence because of the fact that Parliament had done so (whether or not it was a good idea to do so). Moreover, if the institutions of the law had not been prepared to treat the chicken coop as a vehicle, then because of that social fact, it would have been false (after a decision with precedential effect) to say that it was an offence to pull a chicken coop on iron wheels on the road. Law is reflexive in the sense that the law gives legal authority to legal institutions to identify the law. Therefore, the courts’ decisions determine legal rights and obligations. So, we might say, a law is source-based if its existence and content can be identified by reference to social facts alone, without resort to any evaluative argument, other than whatever evaluative argument may be needed to determine the social facts, or to work out their implications for the case at hand.