So far we've dealt with cases where your opponent began with two men ready to be forked by a pawn. One of them may have been an unsuitable target—e.g., an enemy pawn that needed to be upgraded with an exchange—but the basic geometric motif already was present. These next positions differ because the geometry for a pawn fork needs to be created; enemy pieces have to be forced onto squares where they can then be forked. How do you force a piece onto the empty square where you want it to go? Sometimes a threat will do the trick. Normally your opponent will move a threatened piece someplace safe, but if it has a limited range of motion because some of its escape squares are blocked or attacked, a threat may force it where you want it to go. Consider this section a general set of lessons in paying careful attention to where threatened pieces will move.
In this first example White has a pawn that can jump into position to attack the Black queen with g2-g4. The threat is of limited interest by itself, but it would make a terrific first half of a double attack: if Black’s king could be goaded onto f5, White would have a pawn fork. Of course White's knight is there now, and Black's king will want to avoid capturing it precisely because of the fork that then results. But whether these thoughts occur to you or not, on principle you would want to examine every check White can give and its consequences. White has a check at d4 with his knight that achieves nothing. He has checks with the queen at d7 and f7 that lose the queen right away, but another check at e7 where the queen enjoys protection from the knight. How would Black respond? He would have to move the king with KxN. White imagines the board as it would then look and realizes that Black's king and queen would then be forkable with g2-g4.
A loose end remains. When we went over White's checks, we left one out: Re1. It looks good; indeed, it forces the same initial result as Qe7: Black has to play KxN, and now White has that same pawn fork. But there is a grave difference in what follows from there. After White plays g2-g4, Black naturally moves his king away with Kxf4, and then White has g4xQ (the execution of the fork)—but now notice the state of the g-file. White's pawn no longer is there; the only things left behind are White's king and queen: a perfect chance for a pin by Black, which he exploits with Rg8. White can't move his queen, and will lose it next move. White's better starting move, Qe7, avoids this calamity by getting the queen off the g-file right away.
The general lesson of this last variation is to be careful to study all of your checks. Sometimes one looks as good as the next for a purpose on first inspection, but turns out to have quite different side effects. The more specific lesson is to be alert to one particular type of side effect: lines that get opened by a tactical sequence, such as the g-file in this case. This last possibility may seem startling and worrisome if you haven't studied pins; but once you get through that part of this project, you will know that the sight of White's queen and king on the same line is something to notice from the beginning here.