I've been reading some online articles on the concept of "function", but I'm not very sure about it. An ashtray, according to my dictionary, is a "container for cigarette ash", but I don't know what this "for" means. It can't mean that people ought to put ashes in the ashtray, because there are other places where we may put it. And it can't mean that people may put there the ashes, since, once again, we may put the ashes in places which are not ashtrays. It can't either mean that the ashtray was made "with the purpose" of serving as a container for the ashes, because an object may be an ashtray now but haven't been made to be an ashtray. So, what is an ashtray?

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You're right to suspect that the idea of function is somewhat unclear--at least in most uses. In one sense, a thing may be said to "perform a function" just in case it does whatever it is that is within the description of the function. So, a highball glass can "perform the function" of an ashtray, because it can do what we ordinarily associate with the ashtray--that is, serve as a receptacle for ashes.

Something made to be an ashtray would be an object for which serving as a receptacle for ashes would be its "intended function." The intended function of a highball glass (whose intended function was to be a drink container of a certain size and shape) is not to be a receptacle of ashes. So the object whose intended function was X may end up performing some other function.

Now one way in which things can shift functions is because beings capable of forming intentions can decide to change the functions the objects serve, either temporarily or permanently. So we can turn an old tire into a swing, or a highball glass into an ash tray.

Now, a function is not necessarily to be understood in terms of purposes, but may sometimes be best understood in terms of what the thing customarily or ordinarily does, as a matter of fact, or as a matter of the sort of thing it is (call this a "natural function". In this sense of function, a thermostat is "functioning" if it senses temperature and opens and closes a circuit at the appropriate times as a result. Doing this may be the "purpose" of the thermostat (from the point of view of its maker, or user), but it could continue to perform this function even if all sentient life were to disappear, so that it would no longer serve any purpose.

So, an ashtray could be: whatever happens to be used as a receptacle for ashes (performed function), whatever was made to be one (intended function), whatever beings with intentions take to be one (showing their purpose for the object), or whatever normally and customarily serves as one (natural function).

Your question suggests that answers to the question “What is thefunction of X?’ will have normative implications about what we ought orought not, may or may not, do to Xs. And this fact is puzzling. How,you might be wondering, can certain facts about an object’s functionhave any implications about what I may or may not do to it? And I thinkthat you are right to be skeptical: in the case of ashtrays, functionaldefinitions have no normative implications for us– about what we may ormay not do to them.

However, behind your question may be Aristotle’s “function argument” in the Nicomachean Ethics (I 7), where he argues that information about the “function” (ergon) of humans has implications for what sort of life humans ought to live-- “ought”, that is, if they are going to be well off.

Onmy view, Aristotle’s notion of function does not correspond to any ofthe three notions of function that Nick distinguishes for ashtrays. Todistinguish Aristotle’s notion from those that Nick defines, I’ll referto it as an object’s “real function.” On Aristotle’s view, the notionof an object’s real function plays a significant explanatory function. If I want to know why this hammer has the attributes that it has, I have to understand what the hammer is for. If I want to know why hearts have the attributes they have, I have to know what they are for.Hammers and hearts can be used for all sorts of purposes, but not allof these purposes will be equally useful for such explanatory purposes.

The fact that we put objects to uses other than what they arereally for usually doesn’t much matter– sometimes we can put objects tobetter use than we could if we restricted ourselves to using them onlyfor real function. This statue is quite hideous, but it makes for avery effective doorstop. On Aristotle’s view, there is a significantexception to this general rule. While we might put other objects tobetter use than what they are really for, our own selves are adifferent matter altogether. On Aristotle’s view, if we are going tolive the best life, we must perform our real function and do so well.

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