Figure 4.1.2.4[White to move]

This time Black’s e5 knight and his queen both are in line with his king. The knight isn't a suitable target for a pin because it has a white pawn in front of it, but the queen can be pinned on the diagonal with Bb5. Since the queen can slide in all directions, it can attack any piece that pins it; in this case, for example, Black could reply to the pin with QxB. This means that if you want to pin a queen you need protection for the pinning piece. Here the bishop gets protection on its new square from the knight on c3—so if Black does play QxB, White replies NxQ and wins the queen for a bishop. Later we will study more complex positions where protection of this sort must be arranged.