4♣ is Gerber always and only:

  • when the bid is an immediate response to a natural NT bid by partner.

Responses to 4♣ (Gerber)

Response Aces
4♦ 0 or 4
4♥ 1
4♠ 2
4NT 3

Ditto responses at the 5 level to a subsequent 5♣ (Gerber asking for kings);


Examples

West North East South
1NT - 4♣1

1 Gerber


West North East South
1♣ - 1♠ -
2NT 4♣1

1 Gerber


West North East South
1♣ - 2♣ 1 -
3NT 4♣2

1 inverted minor (strong)
2 Gerber. The cost of a simple definition is that Gerber may apply when you prefer it did not.


West North East South
1♣ - 1NT/2NT/3NT -
4♣1

1 Gerber


West North East South
1♣ - 1♥ -
1♠ 3NT
4♣1

1 Gerber


West North East South
1♠ 3♦ 3NT -
4♣ 1

1 Gerber (like it or not)


West North East South
1NT - 2♣ 1 -
2♥ 4♣2

1 Stayman
2 not Gerber. Presumably a slam-interested splinter with heart match.


Notes

  • The simple definition has the benefit of removing any risk of ambiguity, but may create situations where a preferred natural 4♣ is lost.
  • Bridgebums page is confusing. The 2 bulleted definitons are alternate definitions (ie either or, not both!)
  • a quantative invite can be more helpful than Gerber