3...Bg4 is a serious mistake, and against a master it's sufficient to lose the game by force, as Morphy demonstrates. Why is it such a bad move? Black will be forced to capture on f3, conceding not only the bishop pair, but most importantly the two spent tempos for capturing the knight, which has only moved once. Thus white gains one tempo (i.e. the difference) for development.

4...dxe5 5.Qxd8 CHECK! 5...Kxd8 6. Nxe5 winning black's e-pawn because the knight is no longer pinned. Black is then forced to retreat the bishop from g4 in order to defend the f7-pawn, losing time. White continues developing pieces with the initiative and will bring a rook to the d-file (perhaps with check), and black will not find a safe square for his king. Even though the queens have been traded this is a middlegame, not an endgame.

Next, white recaptures with the queen, a developing move. Black has to recapture the pawn which is NOT a developing move.

White has two pieces in play and black has none.

7...Qe7 blocks the bishop on f8 from getting out, and therefore the rook is also shut in on h8. Both of these pieces will be out of play for the rest of the game. However unpleasant this may be for black, the alternative 7...Qd7 loses tactically to 8.Qxb7. The rook on a8 cannot be defended because of 8...Qc6 9.Bb5 pinning and winning black's queen.

Black's idea was 8.Qxb7 Qb4+, exchanging queens. White would probably win the endgame anyway. Many grandmasters (e.g. Capablanca) would have been happy to win a pawn and go into the endgame, but Morphy was an attacking player, and knew that white's initiative would continue to put pressure on black and induce black to make another mistake. 8.Nc3 blocks the check from b4 and now white is really threatening Qxb7.

Not only does Nc3 block the check from b4 and threaten to take the attack onward to d5, but it also protects the pawn at e4. So brilliantly efficient!!

Black's move 8...c6 was more or less forced to defend the b7-pawn. The only alternative 8...b6 would leave black with even more weaknesses than in the game. Note that white has been developing PIECES to good squares and making threats, that have forced black to spend precious time defending with a pawn move (which is NOT a developing move) and a queen move (which is a BAD developing move).

With every move white brings another piece into play. Now white has 4 pieces attacking, and black has only 2 pieces in play - one of which is pinned and the other one is getting in the way. Black CAN'T bring out any more pieces -- 9...Nbd7 drops the b7-pawn and 9...g6 (trying to fianchetto the dark-square bishop and castle) also loses material after 10.Bxf6. The black queen can't guard both the f6-knight and the b7-pawn at the same time.

Black was desperate anyway, and simply couldn't see the refutation. White's lead in development is now overwhelming, but now it is time for white to DO SOMETHING. If white retreats with 10.Be2, then black can try to catch up in development with 10...Nbd7

White sacrifices a piece to open lines and keep the initiative, but is white really behind in material? The f8-bishop and h8-rook are trapped. If you don't count those pieces white is actually AHEAD in material.

Positionally, white is much better. Material doesn't mean much here.

The Nbd7 is PINNED. The Nf6 is PINNED. The Bf8 and Rh8 are TRAPPED. Black's queen is not happy on e7 and the black king is almost smothered by his own pieces. Note: on white's next move he plays 12.O-O-O because it is the most efficient way to develop both of the white rooks as fast as possible; 12.Rd1 or 12.O-O would be slower.

The pinned knight on d7 is attacked twice and therefore has to be defended twice. The black knight on f6 doesn't count as a defender because it is also pinned, and the queen doesn't count because it is too valuable to be traded on d7. White needs to bring one more attacking piece to hit the d7-knight. Which of white's pieces is not attacking yet? What is the fastest way to get it into the attack?

White's rook on d1 was actually in the way of where the h1-rook wanted to go! Morphy solves this problem by sacrifice, instead of doubling rooks with Rd2 or Rd3 followed by Rhd1.

Point count chess: White has queen (9), + 2 B's (6), + R (5), + 7 p's = 27 points Black has 30 points according to the textbooks, but the value of pieces can change according to the position. The rook on d7 can't move at all so we can give it zero points. Same with the bishop on f8 and almost the same with the rook on h8. The f6-knight should be somewhat less than 3 points and the queen should be somewhat less than 9 points. So, my score is 27 points for white and 12 or 15 points for black.

Can you find the forced checkmate from this diagram?