Epsilon is a suit-specific Control Asking Bid used only after a suit has been agreed as trumps in an Asking Bid sequence. It asks what degree of control responder has in the named side-suit. This includes shortages as well as honour cards. Epsilon is never available unless a suit has definitely been agreed as trumps (otherwise neither partner knows what constitutes a side-suit). Once trumps have been agreed, then all trump asks (except clarifying repeats) are unavailable, and Epsilon is the only Asking Bid available (apart from Beta if Responder's exact level of Controls is not yet known).
When is a Bid Epsilon?
In practice, any bid in a side suit once trumps have been agreed is Epsilon unless it is Beta by virtue of Beta's precedence. ie: If trumps have been agreed but responder's exact number of controls is not yet known, then a bid of 4♣ or 4♦ or a Relay in the next suit (See Beta) is Beta rather than Epsilon, but if their exact number of controls is already known then it is Epsilon.
When is a Bid not Epsilon
The only other two times when a bid in a side-suit is not Epsilon are either
A 3rd bid in an Epsilon suit (ie: after an Epsilon and a Repeat Epsilon), or
A jump-shift into a side-suit (whether Epsilon has yet been used or not).
Both of these bids are 100% natural and "to play"
Responses to Epsilon
The responses to Epsilon are as follows (in all cases, holdings and honour cards shown are specific rather than generic):
: No Control [xxx(x)] or 1st and 2nd Round Control [A or AKx(x)]
: 3rd Round Control [xx, Qxx(x) or Qx]
: 2nd Round Control [x, Kxx(x) or K]
: 2nd and 3rd Round Control [Kx, KQx(x) or KQ]
: 1st Round Control [Void or Axx(x)
: 1st and 3rd Round Control [Ax, AQx(x) or AQ]
: 1st, 2nd and 3rd Round Control [AK, AKQx(x) or AKQ
In the instances above (x) denotes any holding longer than the one shown. Thus "Qx" means a doubleton Queen while "Kxx(x)" means at least a 3-card suit with the King but no other Top Honour and "AQ" means exactly Ace-Queen doubleton.
Repeat Epsilon Asks
Opener may make a Repeat Epsilon in the same suit in order to clarify Responder's exact holding in the suit. These repeat asks use terminology of "Shortage", "Honour" and "Both". In the case where 2nd Round Control has been shown, for example, a repeat answer of "shortage" indicates a singleton, "honour" indicates Kxx(x) and "both" indicates a singleton King (ie: both the honour and a shortage. In some cases (ie: where the original Epsilon received a 1-step or 5-step response) the options are slightly different (see below). Where the original Epsilon response showed two degrees of control (eg: 1st & 2nd, or 2nd & 3rd), the Repeat Epsilon is only really asking what kind of control the lower degree is because the higher degree of control must be an honour. The normal responses to a repeat Epsilon are as follows:
: Suit without the Jack
: Suit with the Jack
1-step Response to orginal Epsilon
If Responder made a 1-step response to the original Epsilon (showing No Control or 1st and 2nd Round Control), then these responses are modified as follows:
: No Control [ie: xxx(x)]
: Shortage [ie: Singleton Ace]
: Honour [ie: AKx]
: Suit without the Jack [ie: AKxx(x)]
: Suit with the Jack [ie: AKJx(x)]
Responder already known to have a 4+-card suit
If Responder is already known to have a 4-card or longer holding in this suit (eg: Positive Response to 1♣ or an Intermediate Opening in this suit or a 4441-shape hand has been described by Responder and this is not their short suit, one of the only two times repeat Epsilons are possible when a 4441-shape hand has been shown by Responder), then the repeat Epsilon simply enquires about possession of the Jack irrespective of length and irrespective of what degree of control has already been held, so the responses to the
repeat Epsilon become:
: No Jack
: Jack held
5-step Response to orginal Epsilon
If Responder made a 5-step response to the original Epsilon (showing 1st Round Control without 2nd or 3rd, then there is no "Both" option and the normal responses for the Repeat are shortened as follows:
: Shortage [ie: Void]
: Honour [ie: Axx exactly]
: Suit without the Jack [ie: Axxx(x)]
: Suit with the Jack [ie: AJxx(x)] Note: If Responder has already shown a 3-card or longer suit in this denomination (ie: a Minor suit rebid over a Forcing No Trump), then these steps can be contracted still further by the omission of the 1st step.
For cases when Responder definitely has a 4-card or longer suit, see above.
Second Repeat in Same Suit
As stated above a second "Repeat Epsilon" in the same suit (e: a 3rd bid of the suit by Opener with or without a jump) is not Epsilon, but 100% natural and "to play".
Note: If, however, Responder has shown a singleton or void in the suit and their exact number of controls is not yet known then the bid is not natural and "to play" but (you guessed it) Beta
Epsilon in a Known Singleton Suit
Where a singleton has been shown and Asking Bids have been established in a sequence where a suit has been firmly agreed as trumps, it is possible for the Captain of the hand to ask about the nature of the singleton, but only if Responder's exact number of controls has already been established (ie: the bid is not needed as Beta). This is the only occasion where repeat Epsilons can ever be made when 4441 shape hands have been shown (but see above about asking about possession of the Jack).
(1) In a 4441-shape hand
An Epsilon in the singleton suit when a 4441-shape hand has been shown gets the following responses:-
: x or J
: Q or K
...and for a repeat:
: x or Q (depending on the response to the initial Epsilon)
: J or K (depending on the response to the initial Epsilon)
(2) After a Splinter
Where a shortage has been shown via a splinter which could be either singleton or a void, an Epsilon uses the following steps:
: Singleton Queen or x
: Singleton King
: Singleton Ace
Opener may make as many Epsilon Asks as they wish given the available space to ask safely. Opener must always bear in mind the possibility of a answer more expensive than the one they are expecting (eg: an unexpected void) and if this answer would push the bidding too high then generally they should not ask.
Epsilons are potentially the most useful tool available once slam values have been established. They allow Opener to guard aganst inevitable losers or to ascertain ways in which apparent losers can be avoided or discarded. Opener must always, however, plan Epsilons in such a way that they do get to ask the most important questions and must how to obtain the information most cheaply.
Sometimes, for example, an ask in a more "expensive" suit will obtain the same overall information more cheaply (because the response will be less expensive). Similarly, Opener must always ask themselves if they can afford to ask again and perhaps consider asking in such a way that the most unsatisfactory answer will be affordable.
Lastly, timely analysis of the combinations of honours Responder is likely to have (given their level of Controls and Opener's own holdings) will often lead Opener to realise that one particular Epsilon is actually all they need to ask, because the answer to that will simultaneously settle any number of other outstanding questions they might still have about Responder's holdings.