Ruy Lopez 3. Ba3

I've always wondered what the purpose behind 3. Bb5 is in the Ruy Lopez. The main line shows Black responding with a6, threatening the Bishop. If the Bishop took the Knight, then it might make sense. But in most lines the Bishop just backs off to a4 and is eventually chased off by Black with b5, giving me the impression that the move was useless in the first place. On the other hand Black almost never plays b5 right away, but instead just lets the Bishop sit there staring down the Knight. Why not drive it off and gain tempo? What am I not seeing, for White and Black? [Edit: correction made from Ba3 to Bb5]

Maybe 3.Bb5? Bishop on the field b3 more protected than c4. It can't be attacked by d5 or knight a5-e5. Black play b5 when it's most profitable 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O b5 or later.

 The move b5 by Black is not a free tempo as it appears. It's a positional concession when the extended pawn chain a6-b5 cost Black a constant awareness about how to deal with an upcoming a4! If Black takes on a4 then Whites rook is happy having an open file if he doesn't take then should deal with axb5 axb5 when the pawn on b5 looks bit shaky and makes c5 either urgent! been played or not. All this situation makes Black's game become strategically overextended when he needs to find answers to more than one issues as the game goes on. 

The bad news for Black is that it's not sure life is better if doesn't play b5 either unless " Berlin " is your middle name. 

Now some prophet's will jump in saying that Black can play other defences to avoid b5 or the Berlin, but if these would have guarantee much more, we wouldn't talk about b5 now...

b5 in the Ruy Lopez its a " You cant live with it, but life sucks without it. "

 I am such an idiot. In the first post I asked about the move Ba3, but what I meant was Bb5. Apologies for any confusion that may have caused.

I will tell you what you are seeing as factually and plain as day:  you are seeing book-learned sheeple repeating the same moves millions of folks before them have played; it is uninspiring, unoriginal, uncreative, and downright stupid.  Chess snobs arguing they are "having a theoretical discussion about a 'topic' others have previously explored."  it's so hoity toit it's gay.  You are  brilliant person who made a simple notation mistake.  Be kind to yourself, it is the forgiveness of your very own mistakes that will strengthen you into finding the courage into taking the risks that lead to making them in the first place.  Nimzovitch said the threat's worse than the execution, and white pieces think they are "scaring" black that they "might" take the knight.  Yes, it's a bluff with zero shock value, cuz who gives up the bishop pair, oh and everyone and their parakeet have seen this patzer playbook piles of times.  Dumbest dance ever.  Wonder is best invested on other topics like endgame.  Good luck.   

I do not think that there is a quick answer for this sort of issue. If I remember correctly, the strength of the Ruy Lopez was not apparent to the chess world as a whole (including such giants as Steinitz) until somewhere around 1890.

black is not 'gaining a tempo' by playing b5 because it is not developing. It just puts a pawn on b5. Its not losing a tempo either, because white has to move a bishop rather than develop. As far as tempos go, its neutral.

"... Black almost never plays b5 right away, but instead just lets the Bishop sit there staring down the Knight. Why not drive it off and gain tempo? What am I not seeing, for White and Black? ..." - billyyank

"... [After 1 e4 e5 2 Nf3 Nc6 3 Bb5 a6 4 Ba4, if] he was so inclined, Black could play 4...b5 5.Bb3, with play similar to the Italian Game. Playing 3.Bb5 a6 4.Ba4 b5 5.Bb3 is favorable for White when compared to 3.Bc4 for several reasons. On the b3-square, White's Bishop is less vulnerable than on the c4-square--especially when Black tries variations with the ...d7-d5 shot. Furthermore, the b5-pawn is a potential weakness. White might play a2-a4 to expose such a weakness. ..." - GM Yasser Seirawan (1999)

At the right moment, White will play a4 and Black's Queen-side disintegrates. The Lopez is not really an effort at a quick knockout, but an effort to accumulate small positional advantages until one side pops.

Basically what everyone else is saying about b5 is the problem for Black and why White plays 3.Bb5 instead of say, 3.Bc4.

Another way to think of it is that Black has given White what is called a "hook", and as mentioned, a4 is in the cards, when Black must break up his Queenside with a pawn advance to b4, after which a5 by White would isolate both pawns on a6 and b4.

If, instead of 4.Ba4, White plays 4.Bxc6, he is banking on Black's pawn structure to do him in.  After 4...dxc6 (4...bxc6 makes little sense and is maybe played 1 game out of every 500 to 1000 that the position after 4.Bxc6 appears), White is banking on the crippled pawn majority for Black (4-on-3 on the a-, b-, and c-files) doing him in compared to White's better version of the 4-on-3 on the Kingside.  Clearly White wants an endgame, and almost all King and Pawn endings are winning for White in the Exchange Ruy Lopez.

So the fact that White has the choice of whether to saddle Black with an early commitment to giving White a hook, or to saddle Black with doubled pawns and a crippled majority, is part of the reason the Berlin has become so popular as a drawing weapon.  Instead of 3...a6, Black plays 3...Nf6.  It does tend to be highly drawish, but at the top levels, a draw with Black is a moral victory.  They go for their wins with White.

"... the beauty of chess is that all rules are limited and should just be basic guidelines, and that exceptions are everywhere. ..." - IM Jeremy Silman (~2012)

http://dev.jeremysilman.com/shop/pc/Move-First-Think-Later-77p3741.htm

Here is why BB5 is played 

Because at some point black will have double pawns which is not good, I can message you showing the advantages and disadvantages.

Black would be stuck with an unnecessary isolated pawn.  Plus white can play d4 and transpose to structures similar to the steinitz defense with a tempo in hand.  ...dxc6 is always correct.  

The reason black would capture away from the center in the exchange ruy is because it gains a tempo. faster qside bishop development.

But it slows blacks develop ment

In addition to what Fixing A Hole already said, there is also the fact that taking with the d-pawn gives Black an easier time developing his pieces.  He has the Bishop pair, so it would be better for him for the center to be open.

White does the same thing in a fairly common line of the Petroff:  1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Nxc3 6.dxc3 (NOT 6.bxc3).

Also, taking towards the center should not be viewed as a religion.  In the opening, it can often block your pieces from developing.  In reality, that whole adage came about mostly in fianchetto positions where the pawn on g6, g3, b6, or b3 is captured.  There, the vast majority of the time (I emphasize, vast majority, not "always") you take toward the center.  But also, keep in mind that a Rook pawn is better than a Bishop pawn when going against a Knight, and with multiple pawns on the board, a Rook pawn is harder for the King to chase than the Bishop pawn, but if it gets down to 1 pawn versus 0, like R+P vs R, then a Rook pawn can be bad.  So every scenario is different.

One of the worst things that chess players do is latch too much onto those basic principles.  When you are a 700 player, follow the principles.  By the time you are 1200, you need to be looking at specifics.  Throw principles out the window.  Some principles remain, like control the center.  Even GMs control the center.  But do you think a GM uses the "capture toward the center" to determine whether hxg6 or fxg6 is better?  Heck No!  He is looking at specifics.  Does taking with the h-pawn fatally open up the h-file to his King?  Does taking with the f-pawn fatally weaken the e6-square (or e6-pawn if a black pawn occupies that square)?

No general concept in chess should ever be taken as Gospel!

Perhaps it would be of general interest to look at a 1963 Leonard Barden passage (converted to algebraic): "The Ruy Lopez gives White a more lasting initiative than any other opening resulting from 1 e4 e5. With 2 Nf3 Nc6 3 Bb5, White already sets up pressure against Black's e5-pawn, and this is one of the major Lopez themes. White's attack is usually strengthened by the advance of his other centre pawns to c3 and d4. The intention is to compel Black to play exd4, after which White controls the centre and can attack on either wing. The fact that Black often defends the Lopez by a general advance of his queen's wing's pawns, incidentally chasing away White's bishop, leads to a second underlying idea. White's pawn at e4 is a support point for knight outposts at d5 and f5, and Black's conventional pawn formation at c5, d6 and e5, commits him to guarding d5 and f5 squares with minor pieces. Much apparently slow manoeuvring in this opening is focused round White's efforts to establish a knight securely on one of the key outpost squares, and to use it as a pivot for attack against the black king or for an outflanking invasion with a rook along the a-file."