In this article we shall consider several common sequences and see whether they should be artificial or natural. For example, what about 1♦-P-1♠-2♦? Many of these sequences do not have a standard meaning, but we shall start with some that do.
Responding to a take-out double
1♦-X-1♠-2♠ is natural, with at least five spades, with 1♦-X-1♠-X being for penalties, showing at least four spades.
1♥-X-P-2♥ shows a good hand, usually at least eleven HCPs. If you have hearts here you'd pass or bid 1NT, or possibly try another suit, whilst the cuebid is clearly useful when you have a strong hand and don't know which suit you wish to play in. Similarly, if the doubler later bids the opened suit, that is also artificial. For example, 1♥-X-P-2♦, P-2♥ shows a strong hand wanting further information from partner.
The following sequence came up in a recent county match: 1♦-P-P-X, P-P-1♠-X, P-2♥-P-2♠. Passing out the takeout double in this sequence doesn't show any values, it merely indicates that 1♦-X is likely to be the best spot. The double of 1♠ is for penalties, and partner has pulled because he doesn't have many of them. The 2♠ bid now is showing a hand too strong to overcall 1♠ on the first round. If the strong hand wanted just to make a general forcing bid he'd have to cuebid in diamonds.
The 1NT Overcall
1♥-1NT most people play as a balanced hand with 15-18 points and a heart stop. In contrast, 1♥-P-P-1NT is usually played as balanced with 11-14 points, as you know that partner must have some strength on this auction. The easiest system over this is to pretend you've opened 1NT and play exactly the same as you would to that, so for many people, the sequence 1♥-1NT-P-2♥ will be a transfer to spades. 1♥-1NT-P-2♦ will be a transfer to hearts-possibly not the best of agreements, but simple and easy to remember.
If opponents come in over this, then I think the easiest thing is to do exactly as you would if they'd come in over your 1NT opening. Thus 1♦-1NT-2♣-2♦ will say that you have a desire to play in 2♦ (assuming that 1NT-2♣-2♦ means that, as I hope it does).
What might surprise some players is that 1♦-P-1♠-1NT really ought to be natural also, though stronger, around about 18 or 19 points. Many play this as showing the other two suits, and my experience at Trumpton (as the Cambridge Club Tuesday night meeting is affectionately known) suggests that most people abuse this bid so much that it is worth playing it as natural if only to stop them doing so! Over this sequence, you can again play the same system as over a 1NT opener.
We now come to some sequences where there is little general agreement. The first important principle is that the meaning of a sequence such as 1♦-P-1♠-2♦ should be the same no matter whether 1♦ was natural, showing at least three, or a Precision bid. I recommend that this is natural.
1♦-P-1♠-2♠ is less clear. I like the general rule that bidding opponents suit directly is artificial (except for 1♦-X-1♠-2♠, as discussed earlier). Then waiting and bidding it on the next time round is natural. Thus this must be two-suited. Since 2NT is also two-suited, then a good treatment is to play 2NT as either weak or very strong, and 2♠ as intermediate in strength (both showing at least 5-5). (A good way to remember this is that the higher you bid the more preemptive it is, so you want to do this on the weakest hands.) I actually feel a better treatment is to play 2♠ as showing 4 hearts and 6 clubs, with a fair hand.
In a similar vein, I would suggest that 1♥-P-2♣-2♥ shows 4-6 in spades and diamonds. This sequence may sound similar to 1♦-P-1♠-2♦, which we said was natural, but usually when people respond at the two level they have stronger hands, and a lot of the time the opener will be just about to rebid 2♥. Furthermore, people don't tend to play short major suit openings. 1♥-P-2♣-P, 2♦-P-P-2♥ would then be natural, for you could have bid 2♥ artificially on the previous round.
Sequences such as 1♦-P-1♠-P, 2♦-P-P-2♠, and 1♦-P-1♥-1♠, 2♦-P-P-2♥ are natural, in both cases showing reasonable hands. On the other hand 1♦-P-1NT-2♦ clearly sounds like the majors to me.
Sequences such as 1♥-P-1♠-2♣, 2♠-3♣-P-3♥ are naturalish, in that they are looking for 3NT, showing a heart stop and wondering whether partner has a spade stop. (Thus when you have two cues available you should generally bid your stops, rather than ask for them.)