The "Weak 4's" are extremly aggressive opening bids of  4 ♥  and  4 ♠ . These opening bids commit the partnership to take 10 tricks to a game-level contract, and without an idea of what the partner holds. These are "close-out" bids and the responder should "PASS".

These bids also inhibit the opponents from bidding - their next bid must be at game-level.

These hands hold 9-11 HCPs and hold 8+cards in the named suit. Despite the apparent lack of HCPs and not knowing what the partner holds, it is amazing how often these risky bids are successful.

There are four requirements for these bids:

Point Range:
9-11 HCPs
A minimal hand with 8 or less HCPs is very risky. Strongly consider a PASS with fewer than 9 HCPs.

Suit Length:
Must have 8+cards in the opened suit.

Suit Strength (Critical):
The opened 8-card suit must have at least 5 honor card points (HCPs) (2 of the 3 top honors). Many players forget the honors in the named suit, and end up losing the contract.

Suit Selection:
The weak 4 openings should be used for only major suits  4♥  or  4♠ .

Do not open with a 4-level minor suit.