Iota is a secondary trump asking bid in Opener's main trump suit and asks exactly what holding Responder has in that suit along similar lines to those of Theta.
Iota is used in a number of situations instead of Theta where Responder is either known to have at least a doubleton in the suit, or where it is likely that that is the case (ie: When the Ask is a Repeat Trump Ask in a different suit).
Iota is related to Theta and Delta in that it uses a slightly compressed Theta Scale that initially doesn't admit of Responder having a singleton or void in the suit.
When is a Bid Iota?
Iota is used in the following situations:
If Responder has shown a balanced positive Response to a 1♣ Opening, then any bid that would normally have been Theta is now Iota instead (ie: a simple new suit by Opener after the response to a low-level Beta).
A Repeat Alpha, Delta or Theta in a different suit is always Iota (unless it is in Responder's suit in which case it is Gamma).
Responses to Iota
The responses to Iota are similar to those of Theta but the first two steps are contracted (in all cases, honour cards shown are generic rather than specific) ie:
: Less than Qx or xxx
: Qx or xxx
: KQ or Qxx
: KQx or Qxxx
: xxxxx or xxxxxx
: Qxxxx or Qxxxxx
: KQxxx or KQxxxx
A 3+-step response agrees the suit. Iota is always intended for use with 5-card or longer suits.
Repeat Iota Asks
(1) In the same suit
Whatever Responder's initial response to Iota was, immediate Repeat Iota Asks in the same suit are available below game level and these ask for clarification of Responder's exact holding. Where Responder has shown two alternatives (ie: not a 4 or 6-step
response) then the shorter holding is shown as the 1-step response to the repeat Iota Ask. Opener should not normally need to make a repeat Ask over a 4 or 6-step response to the initial Iota. If they do, however, then this is just asking about possession of the Jack in addition (and the 1-step response denies). A repeat Iota in the same suit always agrees the suit as trumps, whatever length Responder originally showed and whatever their response to the repeat Iota.
[Note: The example above is a very complex Asking Bid sequence and bears close examination, particularly the strategy of not employing Beta, but ascertaining North's hand using Epsilons. This was a good strategy because Beta alone would not give the answers because of the Diamond void in the South hand]
(2) In a different suit
In the event of a response to Iota of less than 3-steps (ie: a negative response) immediate repeat Asks in a different suit are another Iota and are uncondtionally forcing, even at game level.
(3) Repeat Iota in a Second Suit
There is one situation which requires special treatment, the situation being when
Responder has not shown a balanced hand (ie: After a Suit Positive)
Opener has used Alpha, Delta, or a low-level Beta then Theta, and received a negative response and then makes an Iota Ask in a second suit.
The Iota Ask gets a 1-step negative response, showing "Less than Hx or xxx", and
Opener then makes a repeat Iota Ask in the second suit.
This situation is slightly different because we're using Iota in a situation where Responder is not balanced and so might have a singleton or void in the suit. Here, therefore a special 3-step scale has to be used for the repeat Iota:
Singleton or Void
On this scale a 2 or 3-step response agrees the suit. This special scale does not apply when Responder has shown a balanced hand, since "Less than Hx or xxx" always means a small doubleton in those circumstances.
Handing over the Captaincy
(1) Over a Minor Suit
If Opener rebids No Trumps immediately over Responder's response to Iota it is likely that this is at game level, natural, to play if the Iota suit is a Minor. If this is done at the level of 2NT however, it is handing over the Captaincy, perhaps suggesting that stops are bid upwards towards 3NT or simply showing a minimum semi-balanced 1♣ opener.
(2) Over a Major Suit
If Opener takes this course when the Iota suit is a Major, however, it is definitely natural and to play or handing over the Captaincy if responder has made exactly a 3-step response to Iota, suggesting that the combined holding in the Major makes 3NT a better proposition than 4 of the Major. If, however, Responder has shown a better holding than KQ or Qxx, then this is simply a device to invite cue-bids rather than using Asking Bids. As with any action that hands over the Captaincy it allows Responder to take the initiative in whatever way they see fit, but the most likely route is a cuebidding sequence which can be more efficient than Asking Bids, especally if Responder has shown lots of Controls and Opener has relatively few.
Iota is an incredibly useful bid combined with low-level Betas just as Theta. The reason that this route is much more popular than Alpha is because Alpha only tells you whether partner has a predefined measure of what constitutes Support (ie: Qxx or xxxx) or not. Iota, on the other hand, obtains a much more detailed picture of what partner has.
If Opener has AKQxxx in the suit, the chances of Responder having xxxx is small, but xxx is quite sufficient in these circumstances. The Alpha user has to chance making a repeat Alpha in the same suit, hoping that Responder does indeed have a good tolerance whereas the Iota user getting a response of "Qx or xxx" knows immediately that this is the right suit and can make a repeat Iota to force agreement of the suit, knowing beforehand what the response will be. As stated in the pre-amble for Alpha Alpha is best suited to big 2-suited hands where if Responder has no support for the first suit then there is a reasonable chance of support for the second suit.