user23699: I recently learned that this is a valid way for White to play for advantage against the Philidor:
[FEN ""]

1.e4 e5 2.Nf3 d6 3.d4 exd4 4.Qxd4 Nc6 5.Bb5 Bd7 6.Bxc6 Bxc6

According to the Lichess database, White has won 59% of games from this position, while Black has only won 34%. The Masters database also heavily favors White, with 31% White wins / 17% Black wins.
What are the ideas behind White's 4.Qxd4 move, and why does it have such a high winrate? What is White's motivation for violating principles like bringing out his queen very early / giving up the bishop pair?

user18809: Well, why shouldn't it? It's a developping move that recaptures the pawn. "Don't move your queen early" is not really a "principle". The correct "principle" would be "activate your pieces better and faster than your opponent", which often involves some rules of thumb like "don't move your queen early" or "don't move the same piece several times", but some of those "derived rules" are broken in almost all major openings
White has a great spatial advantage, and a lead in development. His pieces have better squares to go to. A quick queenside castling followed by an e5 break could be a threat to deal with.
Anyway please note that 4.Qxd4 scores worse than 4.Nxd4 (ChessTempo's database), so (IF statistics are a valid way to judge it), it's not the best move in that position but rather just another reasonable way to answer 3...exd4?!. 4.Bc4 scores even better by the way!

user921: This position also arises from the Old Steinitz variation of the Ruy Lopez.
[FEN ""]
1. e4 e5 2. Nf3 Nc6 3. Bb5 d6 4. d4 exd4 5. Qxd4

White has achieved the Ruy dream pawn structure and a space advantage. Likely followups are either c4 or Nc3 then Nd5. Black may give back the bishop-pair to eliminate the strong Knight.

user2005: The principle is to not bring out the queen too early when it can be easily attacked.  In this situation there's no easy way for black to attack the queen on d4, so it's not too early.  So instead of being a weakness, the queen in a central square is a huge strength.
A very similar phenomenon happens in the following line of the Scotch game where white develops the queen early and gets a +.6 edge and 43%/21% winrate on lichess.
 [FEN ""]
 1. e4 e5 2.Nf3 Nc6, 3.d4 exd4, 4. Nxd4 Nxd4 5.Qxd4


23699: <p>I recently learned that this is a valid way for White to play for advantage against the Philidor:</p>
<pre><code>[FEN &quot;&quot;]

1.e4 e5 2.Nf3 d6 3.d4 exd4 4.Qxd4 Nc6 5.Bb5 Bd7 6.Bxc6 Bxc6
</code></pre>
<p>According to the Lichess database, White has won 59% of games from this position, while Black has only won 34%. The Masters database also heavily favors White, with 31% White wins / 17% Black wins.</p>
<p>What are the ideas behind White's 4.Qxd4 move, and why does it have such a high winrate? What is White's motivation for violating principles like bringing out his queen very early / giving up the bishop pair?</p>
 18809: <p>Well, why shouldn't it? It's a developping move that recaptures the pawn. &quot;Don't move your queen early&quot; is not really a &quot;principle&quot;. The correct &quot;principle&quot; would be &quot;activate your pieces better and faster than your opponent&quot;, which often involves some rules of thumb like &quot;don't move your queen early&quot; or &quot;don't move the same piece several times&quot;, but some of those &quot;derived rules&quot; are broken in almost all major openings</p>
<p>White has a great spatial advantage, and a lead in development. His pieces have better squares to go to. A quick queenside castling followed by an e5 break could be a threat to deal with.</p>
<p>Anyway please note that <strong>4.Qxd4</strong> scores worse than <strong>4.Nxd4</strong> (ChessTempo's database), so (IF statistics are a valid way to judge it), it's not the best move in that position but rather just another reasonable way to answer <strong>3...exd4?!</strong>. <strong>4.Bc4</strong> scores even better by the way!</p>
 921: <p>This position also arises from the Old Steinitz variation of the Ruy Lopez.</p>
<pre><code>[FEN &quot;&quot;]
1. e4 e5 2. Nf3 Nc6 3. Bb5 d6 4. d4 exd4 5. Qxd4
</code></pre>
<p>White has achieved the Ruy dream pawn structure and a space advantage. Likely followups are either <strong>c4</strong> or <strong>Nc3</strong> then <strong>Nd5</strong>. Black may give back the bishop-pair to eliminate the strong Knight.</p>
 2005: <p>The principle is to not bring out the queen <em>too</em> early when it can be easily attacked.  In this situation there's no easy way for black to attack the queen on d4, so it's not too early.  So instead of being a weakness, the queen in a central square is a huge strength.</p>
<p>A very similar phenomenon happens in the following line of the Scotch game where white develops the queen early and gets a +.6 edge and 43%/21% winrate on lichess.</p>
<pre><code> [FEN &quot;&quot;]
 1. e4 e5 2.Nf3 Nc6, 3.d4 exd4, 4. Nxd4 Nxd4 5.Qxd4
</code></pre>
