The four things you may not drop

Try it on the board

Nothing may be dropped where it could never move

A pawn or a lance may not be dropped on the last rank, and a knight may not be dropped on either of the last two: from there they would have no legal move for the rest of the game.

It is the same rule as compulsory promotion in lesson 4, from the other end. A piece that moves there must promote; a piece that would land there may not be dropped there at all, because a dropped piece is always unpromoted.

Nifu (二歩): one unpromoted pawn per file

You may not drop a pawn onto a file where you already have an unpromoted pawn of your own. Two pawns on one file is nifu, "two pawns", and it is an illegal move - in a tournament, one that loses the game on the spot.

Promoted pawns do not count, so a tokin on a file leaves it open for a fresh pawn. Nor does anything stop your pawn sharing a file with your opponent's. In practice this makes deciding which files to open a real strategic question: every pawn you trade off frees a file for dropping.

• No pawn or lance on the last rank; no knight on the last two.
• Nifu: no second unpromoted pawn on a file you already have one on.
• Uchifuzume: no checkmate delivered by a dropped pawn. Check is fine.
• And the general one from lesson 5: empty squares only, so a drop never captures.

Uchifuzume: you may not mate with a dropped pawn

Dropping a pawn to give check is fine. Dropping a pawn to give checkmate is illegal. Mate with a pawn that was already on the board is fine; mate by moving any other piece is fine; mate by dropping any other piece is fine. Only that one combination is forbidden.

There is no deep logic to it - it is a courtesy rule, several centuries old, that a game should not end to the cheapest piece arriving from nowhere. The board above enforces it: you have a pawn and a gold in hand and a mate in one, and only one of the two pieces is allowed to deliver it. Try both.