Have you ever heard the question “Would you like a tea or a coffee” answered with a simple “Yes”? If so, the respondent almost certainly considers their response to be extremely witty. The questioner is unlikely to agree. There is also a high probability that the joker is someone’s Dad…or perhaps a mathematician.
I have to admit to having indulged in this “joke” in my time (more than once), but until recently it had not occurred to me that it in fact reflects a violation of a general principle of conversation. Enlightenment came when I read the seminal 1975 paper “Logic and Conversation”  by the philosopher H.P.Grice.
The humour (or lack thereof) of the coffee/tea gag lies in the conflict between the logical truth of the statement and its inappropriateness in conversation. While the statement “A or B” is logically true as long as at least one of A and B is true , in the context of conversation, logical truth is not enough. If you knew A was true and B was false, you would not bother saying “A or B”, you would just say “A”. Moreover, that is what others would expect of you. If I ask you to pass me a hammer, I don’t expect you to pass me a hammer and a spanner. In the same way, if you know you are going to Spain for your holidays, I don’t expect you to say “I’m either going to Spain or Canada”, despite the fact that, strictly speaking, it is a true statement. It is this distinction between simple logical truth and appropriateness in conversation that is the subject of Grice’s paper.
Grice bases his ideas on the notion of the “Cooperative Principle”, which he summarises as the requirement to
Make your conversation such as is required, at the stage at which it occurs, by the accepted purpose or direction of the talk exchange in which you are engaged.
People have conversations of many types for many reasons: to do business, to gossip, to seduce, to educate, to inform or simply for the pleasure of conversation itself. In every case, conversation involves (at least) two participants and the conversations that work best are the ones that take the needs of all of the participants into account. So it makes sense that a bit of cooperation is the foundation of a good conversation.
Based on the cooperative principle, Grice goes on to postulate a number of “maxims of conversation”. Here are the maxims as he describes them:
- Make your contribution as informative as is required (for the current purposes of the exchange).
- Do not make your contribution more informative than is required.
- Do not say what you believe to be false.
- Do not say that for which you lack adequate evidence.
- Be relevant.
- Avoid obscurity of expression.
- Avoid ambiguity.
- Be brief (avoid unnecessary prolixity).
- Be orderly.
The term “maxim” is carefully chosen as Grice notes that one need not follow all of the maxims at all times, while still being cooperative. The main reason that a maxim could be violated is if it is in conflict with another maxim. An example would be providing less information than required (violating Quantity 1) because you are not confident you have the facts right (and you don’t want to violate Quality 2).
Viewed in terms of Grice’s maxims, the coffee/tea joke is a clear violation of the first maxim of quantity.
As I have already admitted to this particular breach, the obvious question is: have I violated any other maxims? Some who know me well would take the view that, while I may take pains to avoid a violation of either of the maxims of quality, I regularly and flagrantly violate Quantity 2 and Manner 3 and probably Relation 1. I need to learn to stick to the point or risk being branded an uncooperative conversationalist! Or perhaps it’s too late.
 Available in the collection “Studies in the Way of Words” by H.P.Grice.