What the player types at a prompt in order to produce results in the game world. In the majority of cases, a command consists of an imperative verb, and is sometimes followed by a direct object or prepositional phrase (for example: "get out of bed"). The command may generate an action, but this could fail to happen if, for instance, the command references an object that is not available to be interacted with.
A command determines the actions of the character and the flow of the story. Different commands will yield different outcomes. A player can include several commands on one line by separating them with periods, the word THEN, or a comma followed by the word AND.
(Montfort 2003) distinguishes a command, which tell the player character to do something within the IF world, from a directive (such as "quit" or "verbose") which does not have any meaning within the IF world.
Examples of usual commands
look at/examine something
put something on supporter
put something in container
ask someone about/for something
tell someone about something
talk to someone
show something to someone
Examples of unusual, contextual commands
take a shower
make the bed
Tom, take the key then open the door
attack orc with sword
what is a grue?