The Moon Illusion

A putative conversational implicature that q (from my uttering 'p') is *explicitly* cancelable if, to the form of words the utterance of which putatively implicates that q, it is admissible to add 'but not q,' or 'I do not mean to imply that q,' and it is *contextually* cancelable if one can find a situation in which the utterance of the form of words would simply *not* carry the implicature. 

All conversational implicatures are cancelable. 

Unfortunately, one cannot regard the fulfillment of a cancelability test as decisively establishing the presence of a conversational implicature.

One way in which the test may fail is connected with the possibility of using a word or form of words in a loose or relaxed way. Suppose that two people - Kaufman and his son, say — are observing the moon, which both of them know to be medium large. 

They look at the moon at different times, during the course of the same day, and say such things as

The moon IS bigger now.

Strictly, it would be correct for Kaufman junior to utter things like:

The moon *looks*/*seems* bigger now.

But, by my Oxonian conversational standards, it would be totally unnecessary for Kaufman junior to put in such qualificatory words, since both know (and know that the other knows) that there is no question of a real change of size of the moon — as they see it.