The idea in one sentence
Black pins the knight that would support e4, ready to give the bishop for it to double White's pawns: control of e4 is the theme.
♔ White's plans
- Develop and fight for e4
- Keep the bishop pair if Black takes on c3
- Use the centre after d4 and e3
♚ Black's plans
- Pin with ...Bb4 to stop e4
- Take on c3 when it doubles White's pawns
- Hit the centre with ...d5 and ...c5
Pawn structure. Flexible; often White gets doubled c-pawns or an isolated d-pawn.
How to learn it
- Read the idea and the plans: every move below serves one of them.
- In the story, ask of each move: what does it do, what does it stop, what does it prepare, why not the other one?
- Drill your side. At the key moves you name the idea first, then play the move.
- Missed moves come back first next time, and in your journal.
The defining moves
- 3...Bb4 pins the knight that would support e4.
- 4.e3 solid: it frees the bishop and prepares ♗d3.
- 5...d5 claims the centre.
- 6...c5 hits d4.
The line follows the moves masters play most (Lichess masters database), each checked by Stockfish 19 at depth 22; where the book move is not Stockfish's first choice, the story says so. Scores are in pawns from White's side: +0.30 is good for White, −0.30 for Black.