This chapter gives the definition of ‘category’ in Section 1.1, and follows that by four sections devoted entirely to examples of categories of various kinds. If you have never met the notion of a category before, you should quite quickly read through Definition 1.1.1 and then go to Section 1.2. There you will find some examples of categories that you are familiar with, although you may not have recognized the categorical structure before. In this way you will begin to see what Definition 1.1.1 is getting at. After that you can move around the chapter as you like.

Remember that it is probably better not to start at this page and read each word, sentence, paragraph, …, in turn. Move around a bit. If there is something you don't understand, or don't see the point of, then leave it for a while and come back to it later.

Life isn't linear, but written words are.

Categories defined

This section contains the definition of ‘category’, follows that with a few bits and pieces, and concludes with a discussion of some examples. No examples are looked at in detail, that is done in the remaining four sections. Section 1.2 contains a collection of simpler examples, some of which you will know already. You might want to dip into that section as you read this section.