In legal contexts, a different way of undercutting can also be found. This involves those cases in which a legal norm explicitly includes among its preconditions the absence of an “impeditive fact,” namely, a fact such that if were established, it would prevent the norm’s conclusion being derived (on impeditive facts, see Sartor 1993). This is conveyed by stating that the norm’s consequent follows from certain conditions, unless the impeditive fact holds, or by stating that it follows from such conditions if the impeditive fact is not established. The norm’s consequent can be derived without needing to establish the absence of the impeditive fact, while establishing that fact would prevent that derivation.
Consider, for instance, the rule in Italian law under which a producer is liable when a product it manufactures harms the consumer, unless it is shown that the producer is not at fault (took all reasonable precautions). Here the impeditive fact is the absence of fault on the producer’s side. Let us consider the issue of when John may be liable as the producer of the motorbike which caused Tom’s accident by failing to come to a stop before an obstacle (see Figure 9). It is not necessary to establish John’s fault to determine his liability as a producer. In other words, John’s liability can be presumed by applying this norm (this is denoted by the dotted lines around this premise). However, if it is established that the motorbike was not defective, John may avoid liability.