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 in