A “courtesy bid” is one made by responder on what would normally be considered insufficient values. The idea is to provide partner a second chance to describe his/her hand. For example, a 1NT response to a bid of one of a major ordinarily requires six points. Some people regularly make this bid with four or five.

I tried to use my database of hand records to determine how often this turned out to be a good idea, but the sample size was surprisingly small — only about a dozen or so out of thousands of hands. The results were roughly equally split between positive and negative.

When I did this, I did not take into account which seat the opening bidder was sitting in. The importance of the seating was brought home to me last week in a club game. I was sitting to the left of the dealer with this fine holding:
♠K5 ♥98762 ♦J43 ♣1076.

After three passes my partner opened 1♠. This was followed by another three passes. 1♠ made two, but that was not enough for us to avoid a zero. At the other tables the dealer overcalled his five-card diamond suit, which gave the opener a chance to show his 18HCP and fine heart suit. He held:
♠AQ932 ♥AKQ5 ♦72 ♣K2.

3♥ is easy. 4♥ is makeable if the opponents fail to take two tricks in each minor in the first four tricks. This is not unlikely if partner is playing the contract.

I left grumbling that we had been fixed. However, some reflection made me change my mind. The dealer probably had no more than eleven points; almost everyone opens with twelve these days. Lefty probably had less than ten; he could not find a third-seat bid. So, partner and I must have at least half the deck. I should have responded 1NT because 1) with half the deck and the majority of trumps, we should be safe at the two level; 2) another strain may be better; 3) partner may be looking at a two- or three-suited rock crusher that he did not want to open 2♣.

Note that this reasoning applies no matter how good a hand that responder has. Even if he/she holds a Yarborough, the pair still has half the high-card points. I plan on never passing in this position again, at least with a partner who knows about this tactic.

I have been unable to find anyone who has addressed this issue in print, but the reasoning seems flawless to me. Needless to say, you might get in trouble if dealer has an unbiddable twelve, or lefty has a decent hand with one spade, but those cases should be relatively rare. People today are dying to bid; it is much more likely that partner is sitting on a treasure trove.

The other side of the coin is that when someone in the fourth seat opens, he should be aware that his partner could be very weak. Opener should never jump to game or splinter. A jump shift is enough to show a very strong hand, and it gives responder a chance to apply the brakes.