What is a skewer according to you ?

[arna]

According to the wikipedia page on the skewer, it's an attack upon 2 pieces on the same line but the more valuable piece is in front of the piece of lesser or equal value. Well, to begin with, the sentence "the more valuable piece is in front of the piece of equal value" is a little strange !
Secondly, the reference seems to be The Oxford Companion to Chess (1992), from Hooper, David & Kenneth Whyld. I have never heard of this book but maybe it's because I'm not English. Do you have ?

Ok, let's see what we all agree to call a skewer :


Another one we all agree :


This must be ok too :


But what about this :

Only a pin ?

And finally this :

Only a pin too ?

So, English users, do you 100% agree with the wikipedia description of a skewer ? Is it the way you use it in chess clubs ?
Same question for non-English users : what is a skewer in your country ? Is there a different wikipedia page in your language ?

For all : do you have serious references (books, well known authors or players, etc) on the subject ?

You can use the 5 positions above to speak more easily.

[rmercer]

I agree with the first three. The last two are IMNSHO pins only. No situation should be both a pin and a skewer. Number three is not a pin as there is no penalty for moving the nearer rook.

A pin causes (greater) material loss if the front piece moves. A skewer causes (greater) material loss if the front piece *does not* move.  (Situations with the king in front would be worded differently, but the idea is the same.) When the pieces are the same value as in number three, I prefer to call it a skewer simply because it is not a pin.

[arna]

A pin causes (greater) material loss if the front piece moves. A skewer causes (greater) material loss if the front piece *does not* move.

Rmercer, what are your references ?

Well, medium material loss or greater material loss, both are bad.

The idea of a skewer is to win immediately material, whereas the general idea of a pin is to make use of this pin to gain something, sometimes material.
In a pin, the pinning piece generally doesn't want to take the front piece. In positions 4 and 5, the "pinning" piece wants to ! In these positions, the idea is exactly the same as in a skewer : to win immediately material. For this reason it's sometimes (and in some places, for example in France) called a skewer.
My opinion is that pin is large enough like that, there are many many cases of pin (like explained in the wiki page for pin, and like we can see on chess tempo), so if we can take some of them to "put" in skewer, I think it would not be bad !

[richard]

arna: I think in English the difference in the terms comes from a pin being something that prevents something from moving, (otherwise greater loss occurs) i.e. 'being pinned down'.  Whereas a skewer compels something to move otherwise greater material will be lost. So a pin prevents something from moving, a skewer makes something move.

Richard.

[rmercer]

arna,
You asked "according to you", so I gave my point of view -- no references.

[arna]

Ok Richard. In French it's not very far from that.

Ok Rmercer.

[marvellosity]

Richard's reply seems the right way of looking at it.

[oded ross]

Comments to 59077 (omitting the first ones, who are more confusing than helpful - this is clearly not an x-ray):

In case of pieces of equal value lined up under attack like here, it's a skewer.

   

oded: I'm unsure on that. I think these are half way between pin and skewer, and if anything more like a pin than a skewer, as a skewer usually forces you to move the piece in front to avoid greater material loss, whereas a pin does not, making them more pin like than skewer like IMO.

   

From Wikipedia:
"In fact, a skewer is sometimes described as a "reverse pin"; the difference is that in a skewer, the more valuable piece is in front of the piece of lesser or equal value."
This is agreed upon in chess literature.

   

oded: You should have quoted that full paragraph to give a more complete picture. The next sentence is "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". This is what makes these more like pins than skewers, there is no such compelling here, and irrespective of what wikipedia says, I still think these are slightly more pin like than skewer like, due to the lack of compulsion to move, although they do share features of both. The wikipedia paragraph you do quote is also logically broken. I can't see how it is possible for the 'more valuable piece' to be in front of a 'piece of equal value.' Either it is more valuable or it is equal value, it can't be both.

There seems to be a consensus here about example #3 being a skewer rather than a pin, in spite of moving the rook in front or the one behind to defend the other one making no difference.
Additional sources:
http://www.chess-game-strategies.com/chess-skewer.html
http://books.google.com/books?id=bxRys4yKY1QC&pg=PA201&lpg=PA203
I have at least three more tactic books in Hebrew all stating the same.
And here's a discussion in another chess forum: http://www.chessforums.org/general-chess-discussion/3869-pin-skewer.html

I can find more, but this subject of skewers on equal value pieces isn't discussed very often.

[richard]

There seems to be a consensus here about example #3 being a skewer rather than a pin, in spite of moving the rook in front or the one behind to defend the other one making no difference.

I don't think it is a pin or a skewer, it lacks important features of both, but as stated I think it is more pin like than skewer like, and I don't think it makes sense to try to squeeze it into skewer, as doing so usually makes a nonsense of the definition of skewer. I also don't see the consensus you do, I see consensus that 'a skewer compels something to move', a consensus common in pretty much every definition you'll find, including the ones you've cited below. Diagram 3 clearly doesn't fit this.

Additional sources:
http://www.chess-game-strategies.com/chess-skewer.html

"The aim of the Skewer Attack is to threaten a more-valuable piece into moving, so you can capture a less-valuable piece, which is in a direct line, behind the piece being attacked at the front. "  

Nope. Nothing has to move in diagram 3, move, or not move, loss is the same.

http://books.google.com/books?id=bxRys4yKY1QC&pg=PA201&lpg=PA203

"A skewer, sometimes referred to as an x-ray attack, is sort of a mirror-image pin. It requires a long-range piece and two enemy pieces on the same line of attack, just like a pin does, but in a skewer the more important or powerful piece is doing the shielding. Therefore, instead of immobilizing the piece, a skewer practically forces it to move, thus exposing the poor little guy it had shielded."

Nope. Nothing is forced to move at all in diagram 3. Just because the definition in the book goes on to say skewers include pieces of equal value doesn't change the fact that this definition is inconsistent with the books own definition of skewer.

And here's a discussion in another chess forum: http://www.chessforums.org/general-chess-discussion/3869-pin-skewer.html

That has a mixture of confused ideas, including "In this position it is a skewer because the rook CAN move." Pieces CAN move in PINS too, it just results in material loss if you do (just like in diagram 3) (confusion of absolute versus relative).

I can find more, but this subject of skewers on equal value pieces isn't discussed very often.

While some literature seems to create a special case for pieces of equal value, the special case is almost always inconsistent with their actual definition of skewer, which supports the idea that this situation is not really well described by skewer (due to lacking the urgency of the front piece to move).

[oded ross]

All sources and both forums have an example of equal value pieces lined up under attack, and all say it's a skewer, not a pin. You're too much into the exact wording, instead of looking of what is commonly regarded as a Skewer as opposed to a Pin.
The other forum explains it quite well, especially arabianmate's first post.

[richard]

All sources and both forums have an example of equal value pieces lined up under attack, and all say it's a skewer, not a pin. You're too much into the exact wording, instead of looking of what is commonly regarded as a Skewer as opposed to a Pin.
The other forum explains it quite well, especially arabianmate's first post.

arabianmate's post says "It is a skewer. Think of an actual pin. A pin is used to hold something one place so it cannot move. In this position the rook can move therefore it is not a pin. In wrestling, a pin means that a wrestler is put in a position where he/she can't move. Even though in chess a 'pinned' piece doesn't always means it can't move, however it always means that moving the pinned piece will result in serious consequences. " This is exactly the aspect of diagram #3 that makes me think it has aspects of a pin.  You can't move the rook in the front without 'serious consequences" i.e. it is pin like, of course not moving the pieces also has serious consequences , so it is also skewer like. However it also lacks the key element of every definition of skewer I've seen, that you are moving the front piece because it is more important than the piece behind it.

I think the only reason some sources label this is a skewer is because they haven't really thought through the definitions, and figure it has to be fitted in somewhere so whack it in skewer. I think when you look at all the definitions of skewer, it is pretty clear it is not a good fit for #3.

Richard.

[remiem]

I agree #3 is commonly regarded as skewer. The focus of a skewer is the threat to the piece in the front. A pin on the other hand focuses on the immobility(only considering the pinning piece, the pinned piece and the piece being pinned to) of the piece in the front, but in #3 the rook in the front is just as mobile as the rook behind it.  

[richard]

I agree #3 is commonly regarded as skewer. The focus of a skewer is the threat to the piece in the front. A pin on the other hand focuses on the immobility(only considering the pinning piece, the pinned piece and the piece being pinned to) of the piece in the front, but in #3 the rook in the front is just as mobile as the rook behind it.  

The focus of a skewer is the piece in front RELATIVE to the value of the piece behind. Also the piece in front here is less mobile than other pieces on the board, it can move, but if it does, it exposes the piece behind to attack which is an aspect of a pin. As I say, I don't think it fits perfectly into either definition. It may well be convention to call equal piece situations skewers, but that doesn't make it sensible, it is also convention in some literature to call skewers x-ray attacks (as shown by Oded's book reference), but we don't do that either.

Richard.

[remiem]

1k6/1pp1p1n1/3p2p1/4r3/8/6P1/1Q3PKP/8 w

Imo 1.f4 exploits a pin, not a skewer.

The focus of a skewer is the piece in front RELATIVE to the value of the piece behind.

Skewer
The attacking piece eyes the piece in front and behind. The piece behind is less valuable than the attacking piece or not covered(1st threat).
The piece in front is less valuable than the attacking piece or not covered(2nd threat). If the piece behind is more valuabe than the piece in front, it is a pin. If it is a pin, it isn't a skewer.

Pin
The attacking piece eyes the piece in front and behind. The piece behind is less valuable than the attacking piece or not covered(threat).
The piece in front is immobile, e.g. is less valuable than the piece behind.

Also the piece in front here is less mobile than other pieces on the board, it can move, but if it does, it exposes the piece behind to attack which is an aspect of a pin.

Both rooks are equally mobile.

It may well be convention to call equal piece situations skewers, but that doesn't make it sensible

It's sensible, because it's 1st threat + 2nd threat.

[richard]

Also the piece in front here is less mobile than other pieces on the board, it can move, but if it does, it exposes the piece behind to attack which is an aspect of a pin.

Both rooks are equally mobile.

The front rook is less mobile than other pieces on the board not involved in the tactic, the reason being that it cannot move without exposing the piece behind it to attack, unlike a skewer, it is not compelled to move to avoid a larger material loss, whether you define these as pins or skewers is IMO an arbitrary choice, you can craft the definitions of either to make them fit, but the essence of almost every definition of skewer and pin I've read is that skewer has the valuable piece in front, pin has the valuable piece behind, this makes the discussed situation not quite either.

Richard.