 A related issue involving both uniqueness and existence does deserve attention, however, arising over competition between logics, differing on the rules governing a connective where the first logic has rules which suffice to characterize uniquely a connective and the second has all these and more governing that connective. The standard example of this is provided by intuitionistic logic and classical logic in respect of negation. The fact that the classical rules go beyond the intuitionistic rules and yet the latter already suffice for unique characterization means that there is no ‘live and let live’ option available for the intuitionist, of recognising that the intelligibility of two distinct negation connectives, classical and intuitionistic, which can cohabit in the same proof system each with their respect rules. This should be possible according to those who think that any difference in the logical principles governing a connective reflect a difference as to what is meant by the connective (W. V. Quine’s view—see Section  5  below), since once a difference in meaning is acknowledged, the previously ambiguous connective, “¬”, in the present instance, should be replaceable by connectives registering the disambiguation—¬i and ¬c, say—and the intuitionistic and classical logician should be able to use whichever they take a special interest in, with no further fear of talking at cross-purposes in each other’s company. But of course this is not a possibility, since the rules governing ¬i characterize it uniquely and those governing ¬c duplicate them—think of ¬c as ¬i′, in terms of the above discussion—and do more (securing the provability of ¬c¬cp ≻ p, for example). The result is that the two connectives form equivalent compounds in the reduplicated system and all of the intuitionistically unwanted properties of ¬c spill over to infect ¬i: we can now prove ¬i ¬ip ≻ p, and so on. The conciliatory offer of a purportedly disambiguating notation along these lines is one no advocate of intuitionistic logic can afford to accept. (By imposing restrictions on some of the intuitionistic rules, one can produce candidates for the title of ‘combined classical-and-intuitionistic proof system’—as, for example, in Fariñas del Cerro and Herzig (2001)—but, especially on views according to which the rules of one’s logic articulate the meanings of the connectives they govern, resistance to any such restrictions is entirely understandable. Imagine an encounter with aliens in which they told us that to explain what they meant by some items of their vocabulary we had to be prepared to restrict the principle that ψ followed from φ and ψ for certain choices of ψ involving translations of that vocabulary into English.)