The SCAN: one game, four decisions

Rule 1: when they leave the book, run the SCAN

“I don't know how to play if the opponent deviates from the main line and how to punish him.”

Their move isn't in any video. So what do you know for sure? Everything that matters is on the board in front of you, and four questions get it out. A punishment from a video works against one reply. A procedure works against all of them.

T1 Move two: the queen comes out

Line so far1.e4 e5 2.Qh5

2.Qh5 — Black to move

Their queen is out on move two. Before you touch a piece, run S and A: what did that move change, and what is under attack now?

Your move. Play it on the board — drag a piece, or tap the piece and then the square. Or skip it and see all three.

You will meet this more often than any other surprise: one game in every 21 that starts 1.e4 e5. Run the four questions.

Sthe queen attacks e5 and looks at f7.
Cnothing to take, no checks.
Ae5 is attacked and nothing defends it.
NNc6. It defends e5, brings out a piece, and now their queen is the one in trouble.

The line to avoid: 2... g6 3. Qxe5+ Qe7 4. Qxh8

Rule 2: the opening has three jobs

“It's literally easier to become a rocket scientist than to study all the lines... I've been trying for a year now.”

Get your pieces out. Get your king safe. Connect your rooks. It is the same as leaving the house: keys, wallet, phone. Three things, every time, in any order. Lines die the moment someone deviates - jobs don't.

T2 Move three: nothing clever needed

Line so far1.e4 e5 2.Nf3 Nc6 3.Bc4

3.Bc4 — Black to move

No checks, nothing to take, nothing attacked. This is where the opening does its plain work: pieces out, king safe, rooks connected. Run N and play a move you can give a reason for.

Your move. Play it on the board — drag a piece, or tap the piece and then the square. Or skip it and see all three.

Same game, one move later. The bishop eyes f7 and the position looks sharp, but nothing is attacked yet. This is where the three jobs do the work: bring out a piece and keep the center. Nf6 and Bc5 both do it, and there is nothing to choose between them. What loses ground here is f6 — it blocks your own knight and touches nothing.

Rule 3: run the SCAN on your own move

“The worst blunders always happen after our longest calculation.”

Before you let go of the piece, point the same four questions at your own move. The two mistakes ahead look nothing alike - one drops a rook, the other drags your king into the open - and both come from answering the wrong question.

T3 Move four: the knight jumps at f7

Line so far1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5

4.Ng5 — Black to move

Now something is attacked. Run A before anything else: what is under attack, how many pieces hit it, and what holds it?

Your move. Play it on the board — drag a piece, or tap the piece and then the square. Or skip it and see all three.

Now something is attacked. The knight and the bishop both aim at f7, and f7 has one defender: your king. Run A before you touch anything. The answer is d5, which blocks the bishop and hits back in the center. The move that ignores the question is h6 — it looks useful and does nothing about f7. Then comes 5.Nxf7, forking queen and rook.

The line to avoid: 4... h6 5. Nxf7 Qe7 6. Nxh8

T4 Move five: the recapture two out of three players make

Line so far1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5

5.exd5 — Black to move

You are a pawn down and the pawn is right there. Run A on your own move first: whatever you play, what does it leave loose?

Your move. Play it on the board — drag a piece, or tap the piece and then the square. Or skip it and see all three.

You are a pawn down and the pawn is right there. Run A on your own move first: after Nxd5, what am I leaving loose? f7 again, with one defender. That invites 6.Nxf7, the knight sacrifice that walks your king into the open. 5...Na5 hits the bishop instead and turns the position around: at 1000-1400, players who take on d5 lose far more often than players who play Na5.

The line to avoid: 5... Nxd5 6. Nxf7 Kxf7 7. Qf3+ Ke6

B1 Bonus: what the sacrifice is worth

Line so far1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 Nxd5

5...Nxd5 — White to move

You took the pawn back, and here comes the sacrifice: 6.Nxf7. Play the whole thing out and you meet an honest surprise. On paper White is only a little better here. Yet at 1000-1400 the players who allow this lose far more often, because a king in the open has to be defended move by move. Thirteen moves in, Black owns a knight for a pawn and still stands worse: that king never gets to castle. Objectively fine, practically awful — and that gap is the whole reason a procedure beats a memorized line.

B2 Bonus: a real game, and the move that lost it

Line so far1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 b5 6.Bxb5 Qxd5 7.Nc3 Qxg2 8.Qf3 Qxf3 9.Nxf3

9.Nxf3 — Black to move

This is not a made-up line. Two players rated 1812 and 1877 reached this position on Lichess in June. Run A before anything else: what is attacked, and what holds it? The knight on c6 is pinned by the bishop on b5, and the pawn on e5 is defended by that same pinned knight. Black developed with 9...Bb7 - a normal move that answers neither question. It costs a pawn to 10.Nxe5, because the pinned knight cannot take back.

B3 Bonus: same position, the move that holds

Line so far1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 b5 6.Bxb5 Qxd5 7.Nc3 Qxg2 8.Qf3 Qxf3 9.Nxf3

9.Nxf3 — Black to move

The same position, rewound. A asked two things: the knight on c6 is pinned, and it is the only defender of e5. 9...Bd7 answers both at once. It blocks the line from b5 to c6, so the knight stops being pinned, and it puts a second defender on the square the bishop wants. Now 10.Nxe5 loses a piece instead of winning a pawn. One move, both questions closed - that is what running A buys you.