We will first see what happens when White undertakes the advance
in question on his second move. Superficially the difference
between 2. PQ4 and 2. P-KB4 is that in the first case the pawn
thus advanced is covered, while in the second it is not. An
opening in which a pawn sacrifice is offered, is called a
"gambit"; 2. P-KB4 is therefore a gambit.

2. P-Q4 is only a gambit if after 2. ... PxP White does not
recapture the pawn. Nevertheless this opening has been called the
"centre gambit," and though the denomination is not correct we
will adhere to it, as it is in general use.

A very considerable difference between the centre gambit and the
King's gambit lies in the fact that in the former acceptance is
compulsory, whilst in the second it may be declined.

For: 2. P-Q4 threatens to take the King's Pawn. To defend it by
means of 2. ... P-Q3 is unwise, since White exchanges pawns and
then Queens, by which Black loses his chance of castling and
impedes the development of his Rooks. 2. ... Kt-QB3 is also bad,
since after 3. PxP, KtxP; 4 P-KB4, White drives the Knight away,
gaining a strong hold on the centre, and Black has no
compensation for giving up his centre pawn. It may be mentioned
here that after 2. ... Kt-QB3, 3. P-Q5 would be a useless move,
as to begin with it would be inconsequent, since P-Q4 was played
in order to clear the centre, and moreover it would block up a
diagonal which could be most useful to the King's Bishop.

We conclude now that Black cannot hold his pawn at K4. He must
relinquish the centre by 2. ... PxP. He will now either attempt