Parts vs Attributes

Section Last Updated 17-Dec-2015 12:51

An animal may have legs, a car may have wheels; are legs and wheels attributes or (component) parts?

Firstly, we can say that whilst legs and wheels can be observed, they are not observables: observables are intrinsic characteristics such as length or mass, whose values are independent of any entity identification. However, in order to be able to say, “There’s a leg,” one must have performed an identification whose result is “leg”. Therefore, since one cannot refer to (point at) specific legs or wheels without having previously circumscribed and identified them as entities, they are not independent of identification and so cannot be observables as defined.

Could legs or wheels be tags, the only other kind of characteristic, instead?

Again the answer is no. A tag says something about an entity; what does a leg say about an animal it belongs to other than, “I am the leg of…”, which is clearly a relationship – and relationships require the identification of entities. For “I am the leg of…” to make sense, the leg has to be an identifiable entity, and if it’s an identifiable entity then the most natural conclusion is that it’s a part.

Thus, anything that can be identified as an entity within another entity is a part and not an attribute of the latter.

That having been said, the number of legs possessed by an animal is a characteristic: legs can be counted and thus number of legs is an observable.

Note also that an attribute may itself be compound: the (physical) size of an object might be specified in terms of length, width and height and these might be individual attributes or they might be grouped together as a single size attribute with slots for the three individual values. When an attribute has parts, the parts are not attributes of the attribute, they are just parts of it – but they are attributes of the object, i.e. any part of a compound attribute of an entity is also an attribute of that entity.

Discussion of how one distinguishes an intrinsic, dependent part (such as my liver) from an independent part (the marble I swallowed for a dare) is deferred to another time.

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