I have mentioned categorization in earlier posts, suggesting that it is important. The trouble with the words “category” and “categorization” is that people use them in different and conflicting ways. And that is perhaps why the importance of categorization is not well appreciated.
Ian, over at his “Irreducible Complexity” blog, has just posted something about categories that illustrates the different ways that categorization is used.
Here are two categorizations:
I divide animals into these categories: vertebrates and invertebrates. Of the vertebrates I sub-divide them into mammals, birds, fish, reptiles and amphibians. The mammals I further divide into monotremes, marsupials and placental mammals.
I divide animals into these categories: those I own, those that are dangerous, those I have in a book, those that can be eaten, those my nieces would like on a lunchbox, and those that I’d like to paint.
Which is better? The latter, it seems to me.
I won’t be commenting on Ian’s expressed preference between these. My main goal, in this post, is to explain why these are two very different views of “category” and “categorization.”
Carving up the world
The first example of categorization is what fits reasonably well with the idea expressed by Plato and others, of carving up the world at its seams. I’m not so sure about the seams – I’m inclined to think that we often make our own seams. But that’s an issue for a future post.
Categorization, by carving up the world, is something that we do in our attempts to learn about the world. It is something that we undertake when we start with little knowledge, and want to learn more. It is part of a “divide and conquer” strategy for obtaining knowledge. We see a world that is too complex, so we attempt to divide it into simpler parts that we can deal with. And then, in turn, we divide those parts into still simpler parts. This is a systematic way of learning about the world, of developing ways of discovering what is in the world.
Cataloging what we know
Ian’s second example would be better described as cataloging. It is what we do when we already have a lot of knowledge, and we want to organize that knowledge to best suit the ways that we want to use it. Ian starts his second example with “I divide” but we he describes isn’t really dividing. An animal that he has in a book might also be an animal that can be eaten, or an animal that his nieces would like on their lunchboxes. That idea fits better with cataloging than with categorizing, for in fact we often do cross-indexing in our catalogs.
Categorization in Wikipedia
If we look at the Wikipedia entry on categorization, we see a similar confusion between different meanings of “categorize.” In saying that, I am not criticizing Wikipedia. The wiki entry appropriately reflects a general confusion that is widespread within the literature.
The second and third sentences of the Wikipedia entry say:
Categorization implies that objects are grouped into categories, usually for some specific purpose. Ideally, a category illuminates a relationship between the subjects and objects of knowledge.
This is consistent with the second version of categorization that I have discussed above, and have preferred to think of as cataloging. It is for organizing things that we already know about, organizing with concern about how we will use them.
The following sentence goes on to say:
Categorization is fundamental in language, prediction, inference, decision making and in all kinds of environmental interaction.
It is my contention that it is the first version of categorization that is fundamental in language and prediction. It is fundamental because it has to do with acquiring the knowledge in the first place, knowledge that is prerequisite to being able to apply the second form of categorization.
I will have more to say about categorization, and its relation to perception and cognition, in future posts.