You may see in the chart that Poetry is included under Lyric, which is there to exemplify how each of these categories can be refined even further, all the way down to individual books. The better able you are to categorize the type of book you are reading the better able you will be to recognize what kind of book it is, and therefore the clearer the idea you will have of what kinds of questions and answers you might be expected to deal with when reading it. However, it’s important to note that these categories are just guidelines, and are not to be taken as either prescriptions or exhaustive. It is useful to have a general framework, but books will often fall into multiple categories, or a category of their own — one not included in the above chart. For example, Poetry can belong in Lyric and Epic sometimes, but poems can also be found inside plays, or can be in a category all of their own. There can even be expository poetry (though usually we can just call that bad poetry — an exception to this is Geoffrey K Pullum’s poetic proof Scooping the Loop Snooper).
Our specific purpose in reading a book also influences how we categorize it. This is especially true for Imaginative Literature (i.e., Fiction), since it inevitably includes lots of sociology and history, along with many other elements that could exceed a category like Novel, books that are often written primarily for entertainment. So it’s even more important to know why you are reading a book of Fiction than it is to know why you are reading an Expository book — though, it is important in both cases, that is, if you intend to take what is being communicated seriously.