Forcing and Non-Forcing Bids

This month we will look at what bids are forcing and those which are non-forcing.
Consider this recent tale of woe

E     S     W     N
1♠   Dbl   P      2♥ (with 2 points and 5 hearts)
P     3♣    P      P

Apparently South was furious as they had a big hand. The question is was 3♣ forcing? The answer is an unequivocal NO. When South doubled it could be expected that they held 11 to 18 points. With 19+ points a cue bid would have been the best bid. North has 0 to 9 points, with 10+ points they should jump to 3♥. The 3♣ bid shows a better than opening hand, around 16 to 18 points but is not forcing. North can and should pass with low points, as in this case.
Forcing bids fall into a number of camps. The most obvious are responding to conventional bids such as Takeout doubles, Stayman, Cue bids and Ace ask bids. Then there is the forcing to game bids, the most obvious of these is opening 2♣ with 23+ points. Consider this bidding.
N     S
2♣   2♦ (less than 8 points)
Now any bid by North, apart from 2NT, is forcing and South must bid again. South may pass a 2NT bid if they have little or no points, but should bid again with 3 to 7 points. The point here is if North doesn't want South to pass under any circumstances, then do not bid 2NT. A positive response from South forces the partnership to game with the prospect of slam. Positive responses to other conventional bids are usually game forcing. See the series below.

N     E     S     W
2♦    P     2♠    P                    N has 19 to 21 points and S has 6+ points. All further bids by N & S are forcing until game is reached.
1♦    2♦   P      3♥                  E has 19+ points and W has game going points 6+, forcing.
1♦   Dbl  P      2♥                 W has 10+ points. Good game going prospects unless E is minimum. Forcing for at least one round.
1♦    P    1♠     P                    The 2♥ bid is a reverse bid showing 17+ points. S should look 2♥ for game unless dead minimum, which is shown by minimum level bids by South as the 2♥ bid is forcing for one round.

1♦    P    2♠     P                    Jump shift by S showing 19+ points. Game forcing and looking for possibility of slam.

The most common forcing bid is a change in suit by responder. Whenever responder changes suit this is forcing for at least one round. The exception is when responder had the opportunity to open but didn't, thus limiting their hand to less than opening strength. In this case the opening bidder may pass the new suit response. In the situation where responder has close to an opening hand they need to jump the bidding one level to show this strength.
A change of suit at the lowest possible level by the opener is not forcing, responder may pass if minimum for their bid. If opener wants to encourage responder to bid again then they need to jump the bidding one level.

Finally, a little distribution quiz. Playing Acol, 4 card majors the bidding goes
N 1♣   E Pass   S 1NT   What is South's distribution?