In semantics, Q-based narrowing is narrowing (a reduction in a word's range of meanings) that is caused by Grice's Maxim of Quantity (see Gricean maxims). Q-based narrowing occurs when a word A is a hypernym of a word B — that is, when every instance of B is an example of A. It is then common for the use of A to imply not B. For example, consider the words finger and thumb. A thumb is a kind of finger (hence the phrase ten fingers), but the term finger is not ordinarily applied to it: someone who has hurt their thumb might technically be correct in saying "I hurt my finger", but it would be misleading; the ordinary thing to say is "I hurt my thumb."
The term Q-based narrowing is due to Yale linguist Laurence Horn.