What is the difference between a "category" and a "type"

"Category" and "type" are largely synonymous with regards to their similar meanings. ("Type" obviously has a few other uses.)

The only real difference between the two is that a category feels more like a bucket or classification: Things are filed or stored away in categories. A type is more akin to a label or identification.

My type of man is tall, dark and handsome.

Place this in the loser category.

In both of these examples, you could not switch the words out for the other. This isn't so much a grammatical requirement; people just don't do it.

Also of note, the terms have become absorbed by Computer Science and Mathematics with very specific meanings and purposes. For more information, see the relevant Wikipedia pages for Type and Category.

Rule of thumb: something is usually in a category and of a type.

A type can be a loosely defined collection, while a category is a sharply defined thing with a definite membership test. So he's the rude type, but he is in the rude category only if the rudeness distinction is sharp, so that you can test for rudeness. Sharp decisions are usually considered more arbitrary than loose assessments, because they require selecting a trait or feature and a dividing line.

So you can say he's in the tall category only if the "tall category" is defined by 6-feet and taller, and anything less is not "tall". If there is no dividing line, he's of the tall type. Consider also that something being of a "type" means only that it shares characteristics with the other things of this type:

• "He's in the category of Romanian writers"
• "He's the Rumanian writer type"

The first suggests that he is Romanian, the second suggests that he is only sharing some vague characteristics with them.

When you need to classify a thing, use Type if it can be of only one Type, and Category if can have more than one. Basically Type is a N to 1 relationship (a thing can be of only one Type) and Category is a M to N relationship (a thing can have many categories at the same time).

Category conveys a grouping of similar objects. This is completely arbitrary in nature and one item can belong to many such categories.

While type tends to imply that an object can be identified by a particular attribute or trait. It strongly suggests that you should be able to classify it according to this particular attribute or trait that determines its "type".

An example might be that a book might be categorized into being a drama or a comedy or mystery in that it's entirely subjective. One person could interpret it as a drama while another could interpret it as a mystery. However, an example of a book's type would be fiction and nonfiction. This, unlike a category, isn't subjective and identifies what kind of book it is.