I am late to this post. Notwithstanding the comment from Gilithin, the standard Acol treatment is: - 1S-2C; 2D-2S is giving preference. Very often with only two card support. Responder will be be minimum for the two-level response - typically 10-11 points (the 8-10 range given is too weak, the modern two-over one suggests 10 points, or possibly a good nine). - 1S-2C; 2D-3S is invitational. Around 11 points, but guaranteeing genuine three-card spade support. - 1S-2C; 2D-4S shows game values, but not suggesting slam. - Stronger hands will bid 2H (fourth suit forcing), then support spades.