[pbleighton]

In the beginning there was "open with 13, pass (almost always) with 12)". Now the Rule of 20 seems to be prevalent, at least in the U.S. (though I've read that in Great Britain and elsewhere the Rule of 19 is used - true?).
Questions:
1) In the most common terminology, does the term "Light Opening Bids" refer to the Rule of 20, the Rule of 19, etc? Is the Rule of 20 now considered "sound"?
2) If a partnership playing SAYC or 2/1 decides to use the Rule of 19, should they revise the definition of weak, invitational, and game forcing responses up one point?
3) If the answer to 2) is yes, does this mean that 2/1 is less practical using the Rule of 19, because responder will hold significantly fewer game forcing hands in proportion to 1NT forcing?
4) If the answer to 2) is yes, if a partnership wants to use the Rule of 19 (or eighteen), is it more practical to use it with a strong club system, so that strong hands won't be passed out by a responder with 6 or 7 points?
5) What experience have people had using the Rule of 19 and/or the Rule of 18?

[the hog]

Very difficult to answer this. Largely it depends on geographic and also historical origins. You will find that Americans have a totally different philosophy of bidding to much of the worls apart from the French (isn't that ironic?). Americans believe in what is called a 2 handed game ie sound opening bids, approach forcing. Asians, the Pacific incl NZ, Aust, believe in getting in early and disrupting the opponents. Well, is bridge a 2 or 4 handed game?

Playing 2/1 you do not really need sounder openings IF you have discussed with pd the fact that your opening bids can be a bit light. Playing on line, I have been punished for openinh hands that everyone would open here but Americans don't regard as an opening bid. FWIW, I play the rule of 18 in deciding whether to open, as you will find do many who believe in getting in and out quickly,

Read Cathy Chua's book for an intersting espousal of this philosophy.

[hrothgar]

Quote

In the beginning there was "open with 13, pass (almost always) with 12)". Now the Rule of 20 seems to be prevalent, at least in the U.S. (though I've read that in Great Britain and elsewhere the Rule of 19 is used - true?).
Questions:
1) In the most common terminology, does the term "Light Opening Bids" refer to the Rule of 20, the Rule of 19, etc? Is the Rule of 20 now considered "sound"?
2) If a partnership playing SAYC or 2/1 decides to use the Rule of 19, should they revise the definition of weak, invitational, and game forcing responses up one point?
3) If the answer to 2) is yes, does this mean that 2/1 is less practical using the Rule of 19, because responder will hold significantly fewer game forcing hands in proportion to 1NT forcing?
4) If the answer to 2) is yes, if a partnership wants to use the Rule of 19 (or eighteen), is it more practical to use it with a strong club system, so that strong hands won't be passed out by a responder with 6 or 7 points?
5) What experience have people had using the Rule of 19 and/or the Rule of 18?

You've raised a number of interesting questions.  I'm going to give you my perspective, however, other people's opinions will differ.  

Needless to say, I am a strong proponent of light opening bids.  With this said and done ...

To me, the definition of a "light opening bid" hinges on the relationship between the average strength of all hands dealt and the average strength of a "light opening bid".

Case in point.  Assume that we are using the old fashion Work HCP to evaluate hand strength [A = 4, K = 3, Q = 2, J = 1].  There are 40 HCP in a deck and on average a hand will hold 10 HCP.  Using this metric, I would define a light opening bid as one in which the average strength of a constructive, limited opening bid was approximately 10 HCP.

With this said and done, I think that Work Point Count is very badly flawed for evaluating unbalanced hands.  As a result, I don't much likely evaluation rules derived from these.  In particular, I think that the Rule of 20 which explicitly used Work HCP to judge highly unbalanced hand patterns is pretty silly.

Everyone has their own judgement regarding hand evaluation.  Mine is based on the following.  I use a modified HCP scale based on

A = 3
K = 2
Q = 1
J = .5
T = .2

I upgrade hands where honors are located in long suits.  I also upgrade hands where honors are concentrated in support (old notions regarding supporting honors)

Hands also need at least 6 slam points to open (slam points are based on A = 3, K = 2, Q = 1).  Singleton Aces count as 3 slam points.  Singleton Kings and Queens count as 0 slam points.  Hands with significant extra shape (10 or more cards in the two longest suits) can be opened with only 5 slam points.

In answer to some of your other questions:

I believe that there needs to be some type of relationship between the minimim strength required for an opening bid and the minimum strength required for an absolutely game forcing 2/1 response.  The lighter the minimum requirement for a opening bid, the stronger the requirement for a 2/1 response.  Accordingly, the lighter your opening bids, the more overloaded your forcing NT response.

There are certainly a variety of pairs who combine a very light opening style with game foricng or near game forcing 2/1 responses.  For example, Meckwell uses a 2 minor response to a 1 major opening as game forcing.  However, much of the Meckwell style relies on stellar declarer play to bring home exceedingly questionable 3NT contracts.  

[While Meckwell have an exceeding complete set of bidding agreements, I don't think that their system can be considered as particularly cutting edge anymore.]

Your question #4 actually has more to do with whether it is desirable to play a system based on limited opening bids.  This is another interesting question in its own right that probably deserves its own thread.

[inquiry]

1) In the most common terminology, does the term "Light Opening Bids" refer to the Rule of 20, the Rule of 19, etc? Is the Rule of 20 now considered "sound"? A bare rule of 20 hand would be "considered" sound when you are 4-3-3-3 because you need 13 hcp to open... back you your open iwth 13 statement. With 5-3-3-2 you open with 12 hcp, that is not light of course, but few americans would use the term sound to describe it. Make it 5-4-2-2 now 11 hcp would do. Go to 5-5-2-1, now 10 hcp can be a typical opening bid. Here people not following the rule of 20 would start characterizing a first seat bid based upon 10 hcp as "light". I would not, as I have opened as few at 8 hcp with a 1 of a suit, and proposed just such an opening bid on a hand by jjsb in this forum earlier in this week.

I do not treat any rule of 20 opening hand as "light" with regard to the rest of the bidding. A bare rule of 20 hand is minimum, of course, but I bid normally after opening it. If you want to institute less than rule of 20 opening bids, I have found that the switcing to a weak notrump system, or even a kamakize 1NT system, allows me to open all those balanced yucky miniminums 1NT. Something like 11-14 balanced or 10-12, or 9-13 range works well. This gets the truly light hands without distribution off your chest with one bid, and then I stick with Rule of 20 for suit bids. Alternative, some people play a forcing club system which allows their 1S, 1H, 1D opening bid will have some top limit, like 15 hcp. Now you can open all those scattered 10 point hands to your hearts content.

2) If a partnership playing SAYC or 2/1 decides to use the Rule of 19, should they revise the definition of weak, invitational, and game forcing responses up one point?Lowering the range of an opening bid for SAYC of 2/1 is not so horrible as long as your partner can expect it. The problem that arises though is as you question points out, it increase the dynamic range of the opening bid. So if you opening 1S bid can be from 13 to 22 points (count dist) for instance normally, what does it mean when it can be from 10 to 22 ? Your invites and responses have to fill in an extra 3 point range. I open 1st and 2nd seat sound rule of 20 (that is some 20 hand I don't open, I have posted my adds and subtracts elsewhere). But in 3rd seat, of course, I open rule of 18 and sometimes even less. Of course, opening light in 3rd seat is just normal bridge no matter what you call the rule.  

3) If the answer to 2) is yes, does this mean that 2/1 is less practical using the Rule of 19, because responder will hold significantly fewer game forcing hands in proportion to 1NT forcing? No, 2/1 is not less practical, but becomes more difficult. Playing with a partner who insist on opening very light in first of second seat (I have one partner who never passes with 11 hcp and a flat hand with a five card major, and opens many 10hcp hands), all you need do with 2/1 is increase the minimum requirements for a 2/1 response (increasing your range of 1NT responses). The wider your 1NT forcing hands become, however, the more work you have to put into the follow up auctions.  I would add a convention like BART, and play it even on a 1H-1NT auction.  

4) If the answer to 2) is yes, if a partnership wants to use the Rule of 19 (or eighteen), is it more practical to use it with a strong club system, so that strong hands won't be passed out by a responder with 6 or 7 points? Actually it is better to use a strong hand club, but not to keep partner from passing when your bid when you are strong. (Your partner still has to respond with the same values as if all your opening bids are sound or else it puts to much pressure on your 2C opening bid.) But rather to greatly narrow the range of the opening bid when you don't use the 1C bid. That is, people who open very light hands, lets argue here 8 hcp and 5-4 distribution will be enough  (a rule of 17!!), if their top limit is 15 hcp, they have a opening bid range of 8-15 points, only 8 points. A typical 2/1 player may open 1S with from 13 to 21 (9 point range). A person stretching the opening bid of 1S to as few as 8 or 9 point would have a range from 8 to 21 or 13 hcp (more than a full addition opening hand!!!). It is this wide range, not the minimum that is opened that causes problems in the auction IMHO. The ability to open very lightly is among one of the advantages of forcing club systems.

5) What experience have people had using the Rule of 19 and/or the Rule of 18? I have never played a formalized rule of 19 or rule of 18. But opening these hands in 3rd of 4th seat playing sayc or 2/1 is just fine. However, I do frequently open 10 point or 11 point balanced hands with weak or very weak 1NT (depending upon partner). Opening a  hand with 10 hcp and 4-3-3-3 would be a rule of 17 opener when playing the really weak 1NT, which I don't play much. However, I do open 4-3-3-3 hands with 11 hcp fairly frequently when playing my prefered weak notrump range of 11-14 hcp. Also playing precision, I frequently open 10 hcp hands with 1D when holding 4 D or 1 of a major when holding five cards in that suit, but my precision 2C bid still requires a full 11 hcp.

BTW, I think you will find that as the hcp count goes down, most people begin to abandon the rule of 20 for opening bid, I do not. For instance on the JJSB hand I mentioned earlier, S-J H-AQT8, D-void, C-Q10965432, not one poster agreed with my opening bid of 1C, and I would open 1C if the spade J was the Spade 2. All who disagreed with opening 1C had their reasons... not enough quick tricks, not enough controls, etc. But rule of 20 count with 11 cards in two suits and 9 hcp, good intermediates in CLUBS and HEARTS, make a "solid" vulnerable first seat opening bid for me. I don't even consider this light or close. The only concession I will make after opening this hand is my rebids will be a little different from normal (on the auction 1C-(1S)-2D-(2S)-? I will not double for instance despite my 4 card heart suit, for I surely don't want to give partner a chance to pass 2Sx.