 This is related to Grice’s first maxim of quantity (“Make your contribution as informative as required”) and is held responsible for the inference of so-called scalar implicatures, among others. So from an utterance of “Some students came to the party” it is inferable by default that not all the students came. It is not part of the meaning of ‘some,’ yet, in general — by default from the utterance-type — it is what one would infer in absence of evidence to the contrary. In this case, the heuristic has to be restricted to a set of alternates in a ‘scale,’ so that the use of one implicates the non-applicability of the other.