H. P. Grice and J. O. Urmson on the principle of conversational appositeness

Urmson:

MAXIM 1

Other things being equal, it is best to use the referring expression most likely to secure successful identification by the person(s) to whom the communication is addressed.

Or: 

Try to use a referring expression most likely to secure successful identification by your addressee.



cf. Grice on dossiers and identificatory and non-identificatory uses of definite descriptions based on an overlap of dossiers.

Urmson

MAXIM 2 (principle of conversational appositeness):

Be apposite!

‘Other things being equal, when using a descriptive referring expression, it is best to use the one that is MOST APPOSITE to the TOPIC of discourse.'

Try to use the referring expression that you judge most apposite to the topic of the conversation in which you are engaged!