Ross Woods, 2021

A “category” and a “type” are both ways of defining something and are both notions of the nature of something. However, they are very different:

- A
*category*has a boundary that separates X from non-X; something either is or is not X. This binary way of thinking is the normal way of making definitions and is of course very useful in most situations.

- A
*type*is defined by its ideal form and has no boundary. Real examples tend to resemble the ideal to a greater or lesser extent; something can be very X, not very X, or not X at all. This differs from normal definitions, but it is more useful when dealing with the thinking of people, cultures and organizations.

Paul Hiebert referred to these as “bounded sets” and “centered sets” and applied them to cultures in missiological theory. In that context, centred set thinking refers not to whether someone is close to the ideal, but whether they are moving close to it or further way. If the ideal is X, someone moving closer to it is defined as X even if they are currently far away. Similarly, someone moving away from the ideal is defined as non-X, even if they are currently very close to it.