There are many words in the English language that you need to be Susie Dent* to use correctly. Disinterested and uninterested, elder and older and fewer and less to name three that I struggle with. When today’s hand came up in an EBU online League match I was extremely grateful to have ‘Assumption’ and ‘Presumption’ explained so clearly:

West elected to start with the ♣️8 to the Queen and Ace, and South decided to take an immediate Diamond finesse. This was a good play for several reasons: you find out where you are on the hand, and it opens up some later possibilities of putting West on lead to play Spades. East won and played back the ♦️J.

At this point Declarer had to make the assumption that the Ace of Spades is with East, as otherwise he’ll have very little chance of making. This is a borderline presumption, by the way, as East didn’t shift to a Spade when she was in.

Looking a little bit deeper, we can also presume that East has either the J♠️ or ♠️Q, as West may well have preferred to lead a Spade if he’d been dealt both of those.

So give East, ♠️A,J, ♦️K, J 10 and ♣️Q, and we can safely presume he hasn’t got the ♥️Q too, as that would be an opening bid in any system. South therefore proceeded to finesse West for the trump Queen, and was rewarded with a satisfying +620.