Hand Evaluation – Trump ( Simple Major Raises )
Ambiguity is the killer of any language , the language of Bidding being no exception. In a language, having a word with two different meanings causes confusion. In the early days of Bridge , before 5 card major systems were invented , a simple raise was defined to hold 4 trump. When you had 3 trump , you bid 1NT or with a singleton put partner in a possible Moysean. When 5 card majors came into being , nobody thought to redefine the simple raise to show only 3 trump. The value of the 4 th trump is huge for hand evaluation purposes. The 4th trump detracts from the defensive capabilities & add to the offensive capabilities. Game tries & competitive decision are easier when partner knows the existence of the 4th trump. Why should you have a simple major raise ambiguous as to 3 or 4th trump ? It makes no theoretical sense.
Cohen & Bergen love to compete so they made the «Law of Total Tricks» popular. The idea is simple. The more trump you have , the more tricks your side is capable of taking. A combined 9 trump with simple raise values would make a 3 level contract successful & usually meant that the opponents could make something their way . This is true when neither side owns the auction ( competing ) where one side has HCP’s in the 20-23 range. They built a major suit structure around the «Law of Total Tricks « called Bergen raises. Simple raises were defined as showing 3 card support which assisted them greatly in competing , penalty doubles & game/slam tries. Some people were reluctant to give up 3
/3
as strong jump shifts , splinters or fit showing jumps however.
My partners & I include limit raises in our Jacoby 2NT structure . This frees the double raise to show 4 trump with a minimum ( mildly pre-emptive ) simple raise. The only problem with the «Law of Total Tricks « were the flat hands. 
AQxx 
xxx xxx xxx did not conform to the law even though 4 trump is still better than 3 with the same horrid distribution as it is more likely you have 5 trump tricks. Ilya Kuzkin invented a forcing NT structure which took balanced hands with 4 trump out of the simple raise structure. He calls itJerome named after a little known Calgary hockey player. We play fit showing jumps with other simple raises with 4 trump so there is no need for us to ever make a simple raise with 4 trump. You hold x KQxx Jxxx xxxx with partner opening 1. Bidding two hearts instead of 3 hearts is pitiful bidding in my opinion. Tell partner that you have 4 hearts & not keep that a secret from her. Bidding a pre-emptive raise with 3 trump is beginner bridge or reckless bidding to say the least. Since you lack values , you are telling partner you have trick potential by ruffing. With 3 trump , the more the opponents have for switching to trump or doubling your side. You are also single handedly misleading partner as to your trick taking potential. 3 trump is useful as a defensive hand , so describe your hand in a different manner.
Systemic toys in the majors should tell partner you have at least 4 trump . Preempting with 3 trump , splintering with 3 trump or fit showing jumps with 3 trump serve no purposes other than misleading partner & inviting disaster. I just cringe when I see someone making a systemic Jacoby 2NT or splinter or pre-empt or fit showing jump with 3 trump. There are other ways of showing partner you have 3 trump ! Simple raises , 2/1 or forcing NT all do the job nicely. You hold xxx KQ1098x Jx xx , partner opens 1 . This is not a fit showing jump as your whole hand is one suit. These hands are susceptible to bad trump breaks as usually you need a trump entry when the suit is going to be any good in another contract. Change the hand to xxxx KQ109xx Jx x & it is a perfect fit showing jump. I do not like making fit showing jumps with only 3 of partners suit. Experts on the subject contend that Axx or similar is allowed but I do not like it. More useful as a systemic structure showing 4 trump like a splinter does.
Playing a disciplined simple raise & systemic raise style has a ripple effect through your entire system . Partner knows how many trump you have when you are defending. This brings in the «known count» signaling concept which has been worth its weight in gold for me & my partners for decades. You tell partner exactly how to defend a hand with no guessing or ambiguity. A useful spin off indeed for having a major suit structure based on the law of total tricks . The useful switch principle can do the same work asGartaganis signals when you have studied that method of signaling.