When a player rated below 1800 asks me for some quick pointers I will often start by playing out the first few moves of the Scotch Gambit: 1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Bc4 Bc5. Giving the student the Black pieces I will then play the move 5.Ng5 for White and ask him or her to respond to the threat of taking on f7. The resulting position is shown in the first diagram.
In the early part of the 19th century, chess theory held that attacking moves should always be given priority and that pure defensive moves are to be avoided unless absolutely necessary. Sometimes you must defend of course but if you can find a defensive move that attacks at the same time – well, there's a really strong move for you!
The defenders of long ago who reached this position with Black usually had no difficulty finding the move that followed the thinking of the day: 5...Ne5!? attacking the bishop on c4 and defending f7. But then one day someone found a tactic: 6.Nxf7! Nxf7 7.Bxf7+ Kxf7 8.Qh5+ g6 9.Qxc5 (see the second diagram.) White is temporarily a pawn down but he is recovering the d-pawn since if Black defends with 9...Qf6 then the pawn on c7 is left en prise. With Black's king in an exposed position White has all the chances. A dangerous opening, that Scotch Gambit!
Fast forward to 1855 and a young man named Paul Morphy is playing one of his father's colleagues, a Judge named Alexander Beaufort Meek. Judge Meek adopts the Scotch Gambit and plays the 5.Ng5 line. Morphy thinks for a minute and responds with a new move at that time: 5...Nh6!?. The judge executes the same combination: 6.Nxf7 Nxf7 7.Bxf7+ Kxf7 8.Qh5+ g6 9.Qxc5 (see the third diagram.) Morphy now plays 9...d6 and the Judge is somewhat annoyed to find that he cannot capture White's d-pawn because it is protected. Something has gone wrong... He plays 10.Qb5, which Morphy quickly meets with 10...Re8. It is becoming clear that Black has taken over the initiative and he wins in only 11 more moves.
I can still remember the deep impression these two game fragments made on me when I was a young A-class player. There is no better illustration of the principle of development than Morphy's simple move 6...Nh6, which makes all the difference between a very dubious position and a very promising one. No matter that the knight is oddly placed for a short time; what counts is that the other one stays in place and protects the d-pawn.
If you can find the handful of tournament and match games produced by Paul Morphy a century and a half ago, please set up your board and pieces and replay them for yourself. I would be very surprised if this doesn't cause you to discover new ideas in your own games.