The vast majority of the time, 1
and 1
openings show hands with a real club or diamond suit. Normally we open with one of our longest suit (or 1NT with the appropriate strength and distribution). The only time a problem occurs is when our longest suit is a 4-card major, and
we have the wrong strength to open 1NT.
That means there are only four possible problem distributions:
KQ87 
987 AQ8 QT4
J85 AQJ6 KJ2 AK9
A964 JT65 K4 KQ4
Q985 KQJ4 QJ3 K8
In Standard American, hands 1, 2, and 3 are opened 1, and hand 4 is opened 1. (Always open 1 with 3-3 in the minors.) This style is often called "convenient minor." Some partnerships agree instead to open "better minor" and open hand 1 with 1. Others agree to play a "short club" open all four of these hands with 1.
Outside of North America, bidding a 3-card suit is commonly called a prepared minor opening, because this bid is made in preparation for a easy rebid:
to 1 (or 1 to 1 and you have Hand 1), bid your 4-card major.
-2 or 1-2 and you have a weak hand are you forced to pass and run a slight risk of having only a 7-card fit.
Now, let's go across to the other side of the table, and see whether we need to worry about partner having his suit or not:
If partner rebids his suit, he normally has at least six cards. 1-1-2 and 1-1-2 absolutely promise six cards. 1-1-2 could be a strong 5-card suit. If opener has a minimum 3-1-4-5 or 3-4-1-5, he has to choose between raising spades with three or rebidding clubs with five.
If partner bids a second suit at the 2-level, his first suit is always real, and almost always 5+ cards long. 1-1-2 almost guarantees five diamonds and four clubs. 1-1-2 might be a 1-4-4-4 hand.
Opener's reverse shows extra strength, and promises his first suit is longer than his second. -1-2 is a better opening bid than 1. 1-1-2 promises 5 clubs and 4 diamonds: he would raise hearts or bid spades with a 4-card major, and again, 2-3-4-4 or 3-2-4-4 hands would bid 1NT (and might open 1).
If opener bids one minor and raises the other, he really has both of them. His raise promises 4-card support, and with you'd never open a 3-card minor if you had 4 of the other. If the bidding goes 1-2-3, opener has at least four of each. After 1-1-2, opener likely has 5 clubs and 4 diamonds: a balanced hand might have bid notrump.
If opener raises responder's major, you'll be playing in responder's major suit. After 1-1-2, opener may or may not have a club suit, but it doesn't matter, since the final contract will never be in clubs. (A 3 bid by responder now would ask opener to choose between partscore and game in spades according to how good his clubs are -- it's not an offer play in clubs.)
If opener rebids NT and responder has a balanced hand, you'll be playing in NT. If responder has KJ86 AQ6 K832 J8 and the auction goes 1-1-1NT-3NT, opener might be 3-4-3-3 or 2-3-3-5, but you'd want to be in 3NT either way.
You should still usually assume opener has a real suit unless he tells you otherwise. For instance, suppose you hold KQ965 K73 2 J752. Partner opens 1, you respond 1, partner rebids 1NT. Your next bid should be 2 whether opener has a real club suit or not. Opener will choose between clubs and spades - and if he opened a 3-card club suit, he has to have at least three spades, and will now bid 2.
The one "dangerous" auction, 1-2 / 1-2, is rare. Responder will only raise opener to two if he doesn't have a 4-card major and he has an unbalanced hand and isn't willing to bid 1NT -- this means reponder almost always has 5-card support for this raise.
In summary, if opener
or 1, and