5. Bb5 is the white idea. Look up a database to reveal the point of a3, but there definitely is one (:

I think there can be no doubt that the Four Knights, be it Scotch, Spanish or whatever, just produces an equal game if Black reacts in some decent way.

If Williams´ primary recommendation is the Scotch Four Knights I wonder why he covers a move like 4.a3 at all. Black just plays a reversed Scotch Four Knights with 4...d5 where I know of no line that gives the pawn on a3 any meaning.

However, the good thing is that this illustrates that the Scotch Four Knights is important to know from both sides (!) for anyone willing to play 1.e4 e5 with Black.

Strange that 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.Bb5 Bc5! is not covered by Simon Williams. This is currently a popular and often recommended line for Black.

I think that the line where black plays 4 .. d6 is realy missing.
It iis common line bellow 1900 elo.

About 4 ..Bc5, my books recommends different lines.
Two book goes for Nxe5 at once while one book goes for 0-0 first writing that white scores 61% after the reply 0-0 and now Nxe5.
However computer claims that both lines are equal but maybee whites position is easier to handle in practical play.

One could wonder if it has anything to say about e.g. (4. Bb5) d6 or a6.  In this vein, I wonder what the average strength of people who buy such DVDs is.  I think years ago the target audience was said to be ~1700 players.

Unless I'm missing something the contents given by ChessBase don't seem to cover 4.Bb5 Bc5. Does anybody know any different ? This would seem odd as it is the recommended line in several repertoire books.

Rocket Repertoire: The Four Knights - 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6
01: Introduction [10:56]
Symetrical Variation: 4.Bb5 Bb4 5.0-0 0-0
02: 6.d3 d6 7.Bg5 Bxc3 8.bxc3 Qe7 Game 1 Cheparinov,I - Jakovenko,D [16:40]
03: 6.d3 d6 7.Bg5 Ne7 8.Bxf6 gxf6 9.d4 c6 Game 2 Gurevich,D - Mikhalevski,V [10:50]
04: 6.d3 d6 7.Ne2 Ne7 8.c3 Ba5 9.Ng3 Sg6 10.d4 Bb6 Game 3 Anand,V - Mamedyarov,S [11:00]
Rubinstein Variation: 4.Bb5 Nd4
05: 5.Ba4 c6 6.Nxe5 d5/d6 Game 4 Wei Yi - Rodshtein,M [22:10]
06: 5.Ba4 Bc5 6.Nxe5 0-0 7.Nd3 Bb6 8.e5 c6 Game 5 Motylev,A - Carlsen,M [10:19]
07: 5.Ba4 Bc5 6.Nxe5 0-0 7.Nd3 Bb6 8.e5 Ne8 Game 6 Morozevich,A - Svidler,P [15:00]
08: 5.Nxd4 exd4 6.e5 dxc3 7.exf6 Qxf6 8.dxc3 Bc5/c6/Qe5+ Game 7 Short,N - Kramnik,V [17:43]
09: 4...Bd6 5.0-0/d3 Game 8 Carlsen,M - Aronian,L [11:09]
10: 5.Nxe5 Nxb5/Qe7 Game 9 Short,N - L'Ami,E [12:21]
Four Knights Scotch Variation: 4.d4 exd4 5.Nxd4
11: 5...Bb4 6.Nxc6 bxc6 7.Bd3 0-0 8.0-0 d5 9.exd5 cxd5 10.Bg5 c6 Game 10 Morozevich,A - Kramnik,V [15:20]
12: 5...Bb4 6.Nxc6 bxc6 7.Bd3 0-0 8.0-0 d5 9.exd5 cxd5 10.h3 c6 Game 11 Wang,H - Anand,V [16:23]
13: 5...Bc5 6.Be3 Bb6 7.Qd2 0-0 8.0-0-0 Re8 9.f3 d5 Game 12 Kramnik,V - Aronian,L [13:36]
14: 4...Bb4 and 4...exd4 5.Nxd4 Bb4 6.Nxc6 bxc6 7.Bd3 0-0 8.0-0 Re8 9.Qf3 Rb8 Game 13 Karjakin,S - Aronian,L [19:01]
Interesting ideas
15: 4.d4 exd4 5.Nd5 Nb4/Be7/Nxd5/Nxe4 Game 14 Polovodin,I - Zaitsev,I [18:36]
16: 4.Be2 Game 15 Mihok,O - L'Ami,E [04:48]
17: 4.Nxe5 Nxe5 5.d4 Halloween Gambit Game 16 Klepaczka,T - Olszewski,M [05:44]
18: 4.a3 g6 5.Nxe5 Nxe5 6.d4 Nc6 7.d5 Nb8/Ne5 Game 17 Jones,G - Bae,T [09:24]
19: 4.a3 d5/Be7/Bc5 Game 18 Short,N - Wang Yue [05:51]
20: Various 3rd move options for Black: 3...Bc5/g6/d6/f5 Game 19 Motwani,P - Bathie,N [09:16]
21: 2...Nf6 3.Nc3 Bc5 4.Nxe5 and Conclusion [06:46]