Talk:Extensional definition

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I'm confused. The article currently says: "an extensional definition of the term 'nation of the world' might be given by listing all of the nations of the world, or by giving some other means of recognizing the members of the corresponding class." The latter part (starting with "or") seems too broad, at least on the assumption that an extension definition corresponds to the notion of extension, as opposed to intension. Mcswell (talk) 02:25, 23 March 2009 (UTC)

I concur that this makes no sense. Surely to "give a means to recognise the members of the corresponding class" also encompasses giving an intensional definition? As far as I understand it, an extensional definition is one which simply specifies everything which satisfies it. I don't understand why this is apparently distinct from an "enumerative definition".

Frankly this whole article is a shambles and, as this is such a basic concept, reflects very poorly on philosophy in general. Not only does it lack any examples, it seems unable to give a clear and consistent account of what an "extensional definition" actually is. --86.179.129.40 (talk) 02:55, 12 April 2013 (UTC)

Extensional definition vs. enumerative definition[edit]

What is a good example of an extensional definition which is not an enumerative definition? --Abdull (talk) 22:55, 4 September 2010 (UTC)

recommend removal of this page[edit]

Unless and until the author provides some shred of evidence that "extensional definition" is a recognized and customary sort of definition, this page should be removed; this page appears to be unsubstantiated opinion. See Robinson on Definition, for example, for the generally accepted sorts of definition. All useful definitions establish either the intension or the extension of a term. But neither "extensional definition" nor "intensive definition" (let alone "enumerative definition") is commonly seen as a category or sort of definition.

The accepted term for the sort of definition that defines by pointing to things or to types of things is ostensive definition. As Robinson (and many others) have noted, another instance can always be added to an enumeration of things and another sort of thing can always be added to an enumeration of sorts of things. Exhaustive enumeration of instances may be theoretically possible (see set theory and type theory), but in practice, in an infinite universe, and at least for interesting definitions (a useful definition gives us differentia that make a difference [apologies to Bateson]), we can always discover one more instance in-the-world or we can discover an additional type, particularly in the borderlands between recognized types. The point is, and I think both Abdull and the anonymous 86.179.129.40 would agree, there are no grounds to distinguish a claim of "extensional definition" from a claim of "enumerative definition".

As both Mcswell and 86.179.129.40 noted, "some other means of recognizing the members of the corresponding class" (whatever this word "class" might refer to) describes definition that prescribes an intensional claim. An ostensive definition does not provide any means of recognizing instances of a type or members of a set. Such a definition merely points out things that are, according to the viewpoint and purpose of some observer, within the extension of a stated set: it is up to beholders to figure out, if they can, why those particular pointed-to-things appear together in this set.

The best course is to remove this page and the page titled "enumerative definition". Belastro (talk) 01:27, 31 July 2013 (UTC)