In Being and Time, Heidegger describes a special mode of being for tools when they are in use. He calls it “readiness-to-hand” [Zuhandenheit]. Readiness-to-hand is the kind of being of anything useful. The most common example is a hammer. A fallen log over a stream also has readiness-to-hand as its being when someone uses it to cross the river. There is no requirement that a thing with readiness-to-hand for its mode of being actually be used in a person’s hand. Shoes also have readiness-to-hand because they are used to protect our feet. The essence of readiness-to-hand is usability.
However, more than just being able to be used, readiness-to-hand is manifested in its purest form when the user uses the tool without thinking about the tool at all. Heidegger calls this phenomenon “withdrawal” because the tool, as we use it, withdraws from our consciousness. The tool becomes completely invisible or almost non-existent to the user. As is exists less and less to the user, it is treated as a part of the users body or mind. A well designed tool will be absolutely transparent to the user, allowing them to see clearly the work on which they focus. Heidegger would love the study that indicated that the brain treats tools as temporary body parts.
Within those things that have readiness-to-hand as their being is a special class of tools called “equipment.” Equipment is something more than just useful, its existence is owed to other things to which it references (and which reference it) as it is used. The hammer owes its existence to nails, wood, and other implements of construction. Heidegger calls this system of dependencies a “referential totality.” Equipment must exists within the referential totality of the culture in which it was developed and is used. The fallen log, however, is not equipment unless a path up to it is made and signs pointing to it are posted. The use of a simple fallen log as a bridge makes no reference to other things with readiness-to-hand as their mode of being.
So what about when a tool is broken, or poorly designed such that it does not allow the user to clearly focus on the work? The essence of readiness-to-hand is usability, so a thing that loses its usability must have another mode of being, or so it would seem. Heidegger calls this “unreadiness-to-hand.” He is quick to say, though, that things with unreadiness-to-hand are not a completely without readiness-to-hand because they can still be used for something. This makes me wonder: Is there such a thing as a completely useless thing, or do all physical things have at least some measure of readiness-to-hand as their being?
There is another reason why broken tools have readiness-to-hand. Heidegger says that not only the tool, but also the material — or the “toward-which” that the tool is being used on or for — has readiness-to-hand. A needle and the thread and the fabric all have readiness-to-hand when someone is sewing with them. A thing that can be manipulated into something useful also has readiness-to-hand. The broken tool, then, has simply gone from being a tool to being a material. That broken tool is material which can easily be manipulated into a useful thing.
Heidegger also distinguishes two other situations where a thing can have unreadiness-to-hand. The first is when we need a tool that we do not have available. The missing tool has unreadiness-to-hand while other tools around us, although they have readiness-to-hand, are then quite useless and obnoxious. What good is a nail if you don’t have a hammer? It seems quite useless, but again, it is not totally useless because as soon as you get your hammer you can use the nail and get to work. The last situation in which a thing can have readiness-to-hand is when a thing interrupts or stands in the way of some work we are trying to do.
Now, finally, what is the kind of being of a tool when it is not in use? As it is not in use, it cannot withdraw and be fully manifested as readiness-to-hand. But, as Heidegger has implied in several passages, anything that is usable has readiness-to-hand as its mode of being. The broken hammer obviously cannot be used such that it will withdraw, but it still has some measure of readiness-to-hand. Also, the nail, when no hammer is present, itself has readiness-to-hand while the hammer has unreadiness-to-hand. So although Heidegger himself does not talk mush about tools or equipment when they are not in use, it would seem that he would have to say that they have at least some amount of readiness-to-hand as its mode of being.