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(1) Posted by Steven Dowd [Monday, May 19, 2008 21:01]; edited by Steven Dowd [08-05-19]


In order not to bias the audience, I'll ask the question directly without commentary: how are active and passive sacrifice defined/differentiated, and is their use in the chess problem literature different from general chess literature (Spielmann's definition appears to still be the norm)?

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(2) Posted by Hauke Reddmann [Tuesday, May 20, 2008 18:20]

I can only tell the definition from over-the-board chess:

active - you willingly move to the capture field
passive - the opponent attacks your piece and you let it "hang"

I would be *very* surprised if problem chess would
differ here.

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(3) Posted by [Tuesday, May 20, 2008 21:21]

The only Spielmann definition on sacrifice that I can recall said something
on the lines that it wasn't really necessary that it was sound, as long as it
surprised the opponent, and was difficult to disentangle. That doesn't seem
to be applicable to problems, so I can only assume he further definitions up
his sleeve.

As far as I can judge from (older) problem literature, there is a fairly large
degree of agreement that the active sacrifice drops a guard of a piece (or several),
leaving it en prise. The passive sacrifice is merely the refusal to
guard -- for example, if a piece is en prise in the starting position, and still so
after the key move, the sacrifice of it is passive: sacrifice by omission, rather
than commission so to speak. (Blackburne's Terms and Themes, for instance.)

Harley adds a 'pull sacrifice' in his three-mover book (see the index), but doesn't
seem to say anything about what distinguishes it from the other two. (Could it have to
do with zugzwang?) Haven't figured out myself what he means, so far. But when Harley
talks about sacrifice it seems to be related to key moves only.

I think Spielmann uses the term more appropriately in the definition I mentioned:
there should probably be an element of hope/doubt that the sacrifice will 'work'.
Such hope/doubt does not seem to have a place in modern chess problems ...
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(4) Posted by Siegfried Hornecker [Tuesday, May 20, 2008 21:54]

One thing is interesting - what kind of sacrifice is it, if an already attacked piece sacrifices itself? Maybe something between these both...

What if a pawn promotes and the promoted piece can be taken. Is the pawn or the piece sacrificed? Not that anyone would care about this, but for me it would still be a pawn sacrifice (what if the pawn was attacked and the piece also is by the same piece - rook, king or queen? Does this change anything in definition?).

Sorry for intruding, I find this particularly interesting (to tell the world and me :-) ).
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(5) Posted by Steven Dowd [Wednesday, May 21, 2008 02:39]

Thanks all.

Yes I have seen that occur quite a bit (the moving of an attacked piece to another attacked square); I think it is because it is difficult to construct those positions where a piece nicely floats to a square where it can be taken.

As to promoted pawns, surely that depends. In one problem I did recently only the promotion to S worked - and the piece taken, but if it was promoted to anything else, black's reply would be to not take the piece. Surely that counts as more than a pawn sacrifice.

One reason I asked Anders was that in White's book on Loyd he appears to define passive sacrifice in a very odd way.... it set me to thinking, whereas your definition was the one I had always used.
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(6) Posted by [Wednesday, May 21, 2008 06:37]; edited by [08-05-21]

Steven Dowd writes:
... in White's book on Loyd he appears to define passive sacrifice in a very odd way....

Where is that? I found a distinction between the forced sacrifice (taking a checking
piece or avoiding a short mate) and the optional sacrifice in the sections on
sacrificing problems, but none that used the words active/passive. Are those mentioned
somewhere else?
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(7) Posted by Hauke Reddmann [Sunday, May 25, 2008 18:31]

pull sacrifice (Hineinziehungsopfer): dropping a piece
next to the king pulling it into a mating net.

E.g. the classical Qd8+ followed by a double check Bg5+ and Rd8/Bd8#.
(Any OTB player knows immediately what I'm talking about :-)

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(8) Posted by [Sunday, May 25, 2008 19:46]; edited by [08-05-25]

I think I found it -- I got stuck on the first of the problems
mentioned in Harley's book, but it turned out that it was the
last one that was the clearest (well, to me anyway -- I had locked on to
key move sacrifices), and also actually used the term in context :

K. Hanneman. Skakbladet, October 1919
(= 10+10 )

Mate in 3

1. Rh5
1. ... Rc3 2. Sb3+, Rxb3 3. Bc5#
1. ... Qc3 2. Qe3+, Qxe3 3. Bc5# [?A]
1. ... Bd5 2. Sc6+, Bxc6 3. Bc5# [?A]
1. ... Qd5 2. Re4+, Qxe4 3. Bc5#
1. ... Rf5 2. Qg7+, Rf6 3. Bc5# [?B]
1. ... Qf5 2. Qf4+, Qxf4 3. Bc5#

([?B] is not a sacrifice, and [?A] are not completely
unguarded. Harley adds gxh and g5 as well, but they seem
to be beside the point in this context.)

Still, it's pretty clear from this that it is not a third type of
sacrifice as the structure of the General Index suggested.
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(9) Posted by Hauke Reddmann [Wednesday, May 28, 2008 10:34]

Well, one *could* distinguish three type of sacrifices:

a) Active: White moves his piece to a field where it is unguarded
("unguarded" in the broad sense - e.g. the Pf7 in shepherds mate is
guarded, but attacked twice, so it's effectively unguarded)

b) Mixed: White removes a guard from an attacked piece

c) Passive: Black attacks a piece and White ignores.

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(10) Posted by [Thursday, Jun 26, 2008 18:51]; edited by [08-06-26]

Some time ago, Steven Dowd said:
... in White's book on Loyd he appears to define passive sacrifice in a very odd way... .

I probably stumbled over that definition, or something like it today: In part V of the series
'First Steps in Two-Move Classification' (BCM 1910 p. 450-5), White says that '... there
are passive sacrifices, where only the power or activity of a piece is surrendered; and
there are active sacrifices, where the piece itself is offered to be captured ...', and continues:

'The passive sacrifice is frequently associated with strategic keys, especially with clearance
moves. A piece is banished to some remote square, away from all possibility of usefulness, simply
that a more effective man be brought into service.'

He then cites:

G. Cheney
(= 10+1 )

#2 1. Kg7

with the words ' is necessary for White to sacrifice completely the usefulness of the Rook
and the Bishop on g8 and h8 by playing 1. Kg7.' As neither Rg8 or Bh8 is brought into play again,
they are in effect sacrificed.

However, this distinction does not seem to have survived long: it does not appear in the Simple
Two-Move Themes book (1924). And in the Good-Companion Two-Mover (1922), the distinction is instead
made between direct and indirect sacrifices, which is the same as that mentioned earlier in the thread.
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(11) Posted by Steven Dowd [Thursday, Jun 26, 2008 21:46]

Thanks Anders. I found that same definition from White on the BCPS pages - although I've been struggling to find that (again) as well!
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