An unexpected insight on d-pawn pushes/openings

Intro

This is going to be a tiny post compared with my usual ones, but I heard something that lit so many LEDs in my head that I had to share it with you guys.

In a video about the Caro-Kann, GM Igor Smirnov made a minor comment that suddenly gave me an insight into something I have been struggling to comprehend for a long time: why the d-pawn?

The oldest debate

One of the first questions in chess, perhaps the oldest and most debated, is what kind of opening to choose. And based on the geometry of the chessboard, one of the strongest principles in the game is control of the center, so at one point or another you have to ask yourself: do I push the d-pawn or the e-pawn?

And we know Fischer's "best by test" quote and we've heard that e4 openings are "more aggressive" and d4 "more positional", but what the hell does that mean? In hindsight, the term aggressive gives it away as it implies two things: stronger attack at the detriment of defense, implying that e4 openings leave you open in some regards that d4 openings do not.

So what is the d-pawn protecting?

The insight

Igor just said it matter-of-factly because he probably finds this so obvious it needs no explanation, but for total noobs it is gold. He said that a d5 pawn defends the f7 square.

But how? By preventing Bc4, Qb3 and other types of attacks on the a2-g8 diagonal! This applies to White as well, where the d4 pawn similarly protects f2. The second rank f square is the weakest and most vulnerable and often the target of attacks from the other side and a d-pawn pushed forward two squares defends it.

An e4 or e5 push, on the other hand, removes a possible protector of the f square and leaves it more vulnerable.

And before you smugly comment about how apparent this is, won't somebody please think of the noobs?! There is no mention of this concept in the d4 chess opening Wiki, not in the e4 one. It's all about "controlling squares" and "controlling the center", like some sociopath discussing the new world order. I've watched a lot of videos and read a lot of chess articles and this is the first time the idea of the d-pawn defending something entered my consciousness.

In a more general sense, any pawn protects the squares behind it on the diagonals it is placed on, a squared-jaw (pardon the pun) hero saying "get behind me!". We can then extrapolate to any pawn pushed two squares from start and see that they protect only well defended squares, all except the d-pawn which blocks a very important diagonal towards the king only defended f square.

Conclusion

Normally, here I should launch myself into a comparative analysis between various openings and positions where the d-pawn is essential in preventing powerful attacks against the king, but I am not that confident I would do it justice. In this post I simply wanted to share with you my insight and hope it helps.

Let me know what you think.