Of Mice and Men

Actually, this is about forks, pins and skewers, not mice and men other than I'm using a mouse and men may read and comment.  

After a brief conversation with the ever insightful RedGirlz on this subject in another thread.  I gave this topic some thought. 

Chess terms are often not definitive - this is to say, they have been defined in different ways throughout time by various individuals and there is no officially accepted definitions for many of them.  I didn't want to do a historical survey, but I did want to see how some of these definitions stacked up against my own understanding of them.

To me the fork is a curious tactic.

When I first pondered it, I felt a real fork required a piece that can move in two directions (not just opposite or reverse directions). This eliminates the Rook and the Bishop. So in that light a Knight, pawn, Queen and even a King could  fork.  Rooks and Bishops (along with the Queen), however, can pin, skewer and x-ray.  All these tactics involve dual (or more) attacks - that is, one of the attacked pieces will usually be doomed to capture (of course, it doesn't always work out that way -one of the things that makes chess fun are the surprises). So defining each of these tactics, the double-attack can almost be understood but the concepts that differentiate them must be explored.

Wiki defines a fork as "a tactic whereby a single piece makes two or more direct attacks simultaneously."   With the inclusion of the word "direct" I'm inclined to agree with this definition. 

Now it gets interesting. 

Fred Wilson and Bruce Alberston in "303 Tricky Chess Tactics" give this definition of a fork that includes Bishops and Rooks:

Here is a clever example of  a Bishop fork:

Here is an example they give of a Rook fork - the fork-ness of it is less clear to me:

"Chess Tactics for Champions" by Susan Polgar and Paul Truong also concurs that any piece can fork:


Hooper and Whyld's Encyclodedia agrees and simply states:

Wiki defines skewer as "in a skewer, the attacked pieces are in a continuous line. The opponent is compelled to move the more valuable piece to avoid its capture, thereby exposing the less valuable piece which can then be captured."   Again, this makes sense to me to a degree.    I say possibly.
By, "less valuable" it could be assumed the definition means its absolute value or point value - a Rook is more valuable than a Bishop; a Queen is more valuable than a Rook, etc.  But thetrue value of a piece is sometimes determined by the board - hence Queen sacs.
So, I find the term "less valuable" a bit ambiguous. Rather than worrying about the absolute or relative value of a piece in defining which piece is being attacked in a skewer, the term "targeted piece" makes more sense to me.    In a series of articles about middlegame tactics, based on a book by Harkness and Chernev called, "Invitation to Chess" and published over a period of time during 1946-7 in "Chess Life & Review," Harkness differniates between a pin vs x-ray as such:

Wilson and Alberston define the pin:


Hooper and Whyld define the pin:

Personally, I don't view a pin as an attack as such and align myself closer to Hooper and Whyld. The pi,. as I see it, is a device, the sole purpose of which is to hold an enemy's piece immobile for whatever reason.  An attack can ensue and even be made possible because of the pin, but the pin itself is not an attack. The one exception I can envision is if the piece doing the pinning is less valuable than both the pinned piece and the x-rayed piece. e.g., a Bishop pinning a rook to a Queen... then the Bishop will probably at least win the exchange by direct attack - but I'm not sure a pin-like situation where the pin-power -i.e. immobilization-  isn't employed can even be called a pin.

In discussing his own definition of a pin vs an x-ray or skewer, using piece value as a criterion, Harkness gets a bit cloudy when the pinned piece and the x-rayed piece are of equal value. In that instance he cites the non-compulsion to move either piece. But I tend to believe there is a compulsion that makes moving one piece over the other desirable. He goes on to say that a pin only makes sense if the "screened" or x-rayed piece in more valuable... and therefore an x-ray can  target pieces of greater or equal value.

Hooper and Whyld ignore the idea of piece value completely in their definition - They don't include x-ray as a term, giving me the impression that it is indeed an American term. Edward Winter, in fact, wrote: "Another term for skewer in English (particularly in the United States) is x-ray attack."  Hooper and Whyld's skewer definition for x-ray somewhat matches my own broader interpretation:

Back to the curiosity of forks -

In 1841 George Walker in "The Chess Player" called a Knight fork a divergent check (however,by definition, a divergent check checks the King and one other piece - it's not a universal fork) .  However, he goes on to say it is sometimes called a fork and any piece can perform this tactic:

Yet.... the idea of a fork seems to have changed somewhat, becoming limited to referring to a pawn fork:

"The Book of Chess" by George H.Selkirk,  1868:



"Chess: Theory & Practice: Containing the Laws & History of the Game" by the late Howard Staunton,  1876:



"A Complete Guide to the Game of Chess" by H.F.L.Meyer,  1882:

However, after the turn of the century, we start seeing the definition back to including pieces, apparently harking back the Geo. Walker:

"The Chess Amateur," 1907 :

Thanks!...but I prefer eating with a spoon!

Consider this being spoon-fed.

Wahahaha! You are quick on your feet!

I don't see the logic of assuming the B and R cannot fork. You already accept a pawn can, and a B has the ability to attack two squares in the same manner.

A fork attacks two pieces at the same time. B and R can do that just as well as a Q or a N

As I stated, that was my original rumination - I learned better.

"B has the ability to attack two squares in the same manner."  my original thought was that a pawn arrive on a square moving vertically then forks diagonally.  A Bishop is already on a diagonal line and attacks everything on that line, so moving to a new square on that diagonal, it can't suddenly attack two pieces. What I didn't see originally was the possibility of capturing a piece/pawn, enabling the sudden dual attack (as in the example). The logic of the pawn fork doesn't apply to the Bishop.

@batgirl - great read as always, thank you!

@kamalakanta - what about wooden sticks, they could emulate fork on chessboard as well

As per Averbakh all chess is about multiple attack and "combined" attack (attack plus restriction of movement of enemy pieces, when a single attack may be sufficient).

All the above terms, pin, skewer, etc. are in effect just variants of multiple attack.

Multiple means any combination of direct and threat of attack (one move away). Following that logic the above definition of fork (double attack) could extend to direct attack to an enemy piece together with a threat of attack from a square.

Pin is actually a double attack consisting of a direct attack to the blockading piece and a threat of attack on the piece behind it.

Generalization might help sometimes

good point, Coffee_Player!

Nope.  Probably a good thing I don't.

I remember reading someone - in fact I thought it was Averbakh -- who said all tactics are based upon the double attack.  Another variation of a theme?

I don't think a pin actually threatens the screened piece except technically - that is, to make the pin work.  The real threat, if applied, is to the pinned piece which can be additionally attacked but pins are more often used just to immobilize a piece to keep it from taking part in some activity.

Do they teach history at tournaments?

I get the feeling batgirl would make a good archivist , I mentioned that before but batgirl didn't respond so I didn't pursue the "what is batgirls job" thinking further

Quite the contrary, the real target of pin is the screened piece, that's why the blocker is immobilized and then you can put more pressure on it as you say, to cash on in.

What do you think about the phrase " ... two or possibly more threats..." @batgirl

I gave a very critical review (two stars of five IIRC) on Amazon of a book because the author claimed that only a knight can fork. I have long regarded a fork as any attack in two or more directions by one piece. In contrast, pins, skewers, x-rays, and discoveries occur because pieces are on a line--rank, file, or diagonal.

BTW, the Steinbeck novel is worth reading.

Odd title for this article although in Chess our best laid schemes often go awry as in life.