Playing 1D - 2C as a game force makes invitational responding hands with clubs awkward to develop. One common solution to this is 1D - 3C, but it precludes playing 2NT and the 3C response might have more important uses (e.g. the two-way raise that we play.) Here’s one way to capture these invitational club hands within the 1D - 2C structure …
1D - 2C
2D - 3C
3C shows about 11 points, long clubs and is not forcing.
1D - 2C
2NT
2NT shows 11-13 and can be passed. Opener could have 4441. If responder continues he is showing a game going hand. All other 1D - 2C auctions are forcing to game.
A strong 2C response needn’t preclude a four card major. It can be difficult to show the clubs later after a 1H or 1S response so factor that into your response decision. With 4-6 and game strength it is generally best to start with 2C. Here’s how these auctions develop …
1D - 2C
2D
Opener’s 2D rebid is automatic on opening hands with five or more diamonds. Responder rebids 3C with the invitational strength club hand (that was unsuited for an initial 2NT response.) All other rebids show game strength. 2H and 2S are used to locate a 4-4 major suit fit.
1D - 2C
2M
Opener has more than a minimum (14+) and a four card major (and only four diamonds). Game forcing.
1D - 2C
2NT
With a minimum (11-13) balanced hand, or 4441, opener’s 2NT is suggesting a final contract. Can be passed, but any further action by responder, including 3C, is game forcing. (Note, opener could also be weak with 2245, not wanting to force with 3C. This should be very rare opposite responder’s club stack so not having a great solution isn’t likely to be much of a problem. Opener could also fib on this hand, rebidding 2D with just 4, or, maybe consider opening 1C to avoid this admittedly rare situation.)
1D - 2C
3C
This is a forcing raise with 14+ points, 4+ clubs and no singleton or void. One awkward distribution for this system is 3343 with 14+ points. A 3C raise is possible but a better solution is often to open this hand 1C.
1D - 2C
3D
16+ points and 6+ diamonds.
1D - 2C
3H/S
Splinter club raise. This can be bid with a minimum opener on something like 1345, as the shortness compensates for the limited values.