Pins of pieces may facilitate mating attacks, of course, just as pins of pawns do. The patterns that can arise from pinned pieces are more various; to see them you need to be alert to different ways of delivering mate. Later chapters cover mating patterns in some detail, but in our work so far we have been focusing on two general sorts of ideas. First are mates where two or more of your pieces are coordinated in attacking a square next to the enemy king—most often a “queen-plus” mate where the queen lands next to the king and has cover from another piece, such as a bishop, though we also have seen “rook-plus” mates with the bishop on occasion. (The previous position involved a threat of a queen-plus mate on g2, then a rook-plus mate on h1.) The usual way for your opponent to defend against this possibility is to keep a friendly piece near the king to protect the squares on which your queen might like to land. Sometimes you can pin that guard, however, making a safe landing for your queen or rook possible.
Another pattern we have been using, and will see again here, arises when the enemy king is trapped on the back rank and you are able to plant a rook or queen there. A common defense against this threat involves pieces that can be interposed on the back rank if hostile pieces are put there; and again those interposing pieces sometimes can be pinned, making the mate possible after all.
The position on the left can be understood as a back rank mate or a queen-plus mate. The key point to see is that White has a battery of queen and rook on the d-file, trained on a square adjacent to Black’s king. The critical square—d8—appears to be attacked twice by White and defended twice by Black, by his bishop and the queen behind it (setting aside the king’s protection of the square). But on inspection of the king’s lines the e7 bishop is seen to be pinned by White’s other rook. White thus is free to play Qd8#, ending the game.