pre emptive defensive bidding in bridge
This is not really an artificial bid in the strictest sense of the word but I couldn't think of where else to put it!. Pre emptive bids should be used with great care and will very often lead to the bidder going down on the contract. In fact the maxim should be that you make a pre emptive bid with the expectation of going down.
The whole point of a pre emptive bid is not to score points but to stop the opponents bidding. Imagine being first bidder and picking up the hand above. It only has nine high card points and you can be certain that because you have so few points someone will bid so this is your chance to stop them.
With the above hand you open three hearts! If the next player was thinking of bidding they are almost certainly going to think twice.
Your partner would normally pass this type of bid but just imagine if they hold a load of points and a couple of hearts. They would, of course, raise to game and bid four hearts.
Before making a pre-emptive bid you should check if you are vunerable. Going a couple down non vunerable will only cost a hundred points but vunerable if would score two hundred.
The generaly accepted rules for making a pre-emptive bid is that you should hold 7, 8 or 9 cards of the suit and 7, 8 or 9 High Card Points thus: 7 cards with 9 points, 8 cards with 8 points and 9 cards with 7 points.
As this type of bid is designed to stop the opponents from bidding, if you are not the opening bidder you can't use it and any bid after the opponents have bid should be treated as natural.