Rebutting and Undercutting in the Legal
Domain
Let us now us take up rebutting and undercutting in the legal domain.
Consider three norms dealing with civil liability (they are somewhat
simplified versions of rules contained in the Italian Civil code, note
that I assume that all such norms express the presumptive conditional
connection “then presumably”, which is abbreviated as
\(\text{then}^{p}\) in the figures): the first rule (D1) says that those
who cause damage to another through their fault are presumably liable,
the second (D2) that persons lacking capacity are presumably not liable,
and the third (D3) that the incapacity exception presumably does not
apply to those who find themselves in a state of incapacity through
their own fault (see Figure 8). Assume that we know that John culpably
caused damage to Tom (e.g., by deliberately smashing his car). On the
basis of this information and of the first norm, we can conclude that
John is liable to pay damages (argument A). However, assume that it
appears that John lacked capacity at the time of the incident. Then we
can have an argument as to why John is not liable (argument B). Indeed,
the incapacity exception takes priority over the general liability rule,
such that argument B defeats argument A without being defeated by it.
Assume, however, that John’s incapacity was due to his fault, e.g., to
his taking illegal drugs. This provides us with a third argument
(C ) that undercuts (makes irrelevant) the incapacity exception.