To classify means to divide something into groups or categories. The classification is normally made according to one or more criteria. It is often necessary in academic English to classify something you are writing about in order to make comparisons and draw conclusions. This could be done in one or two sentences, a paragraph, or even a whole essay. This page gives information about how to classify, language for classification, and essay structure (if the classification is used for a whole essay).

How to classify

When classifying something, it is important to understand what criterion (or criteria, if there is more than one) that you are using to divide the thing into different groups. There may be more than one way to classify, and you will need to choose the criteria which make most sense for what you are writing about. For example, if you were to classify students in a university class, they could be divided according to any of the following criteria:

• gender
• age
• nationality
• ethnicity
• favourite colour

Classifying according to gender would divide the students into 'male' and 'female'. Dividing according to age is more complex, as you may need to specify age ranges, for example 'between 18 and 21', 'between 22 and 25', etc.

Language for classifying

The language used for classifying depends on whether you are describing the criterion or the result of applying the criterion. Compare the following examples.

• The students in the class can be classified according to gender. [criterion]
• The students in the class can be classified into male and female. [result]

The phrase 'according to' shows that you are talking about the criterion, while the word 'into' shows you are talking about the result. The following are further examples of language for classification using a criterion.

• The students in the class may be classified on the basis of gender. [criterion]
• The students in the class can be classified depending on gender. [criterion]

The following are further examples of language for classification showing the result.

• Economics consists of two kinds: micro-economics and macro-economics. [result]
• Economics consists of micro-economics and macro-economics. [result]
• Economics comprises micro-economics and macro-economics. [result]

It may be necessary to classify when there is no name for the criterion you are using. For example, you may wish to divide a group into Asian and non-Asian students, but there is no category 'Asian-ness' which you can use as your criterion. In this case, you can use the construction 'according to whether... or not' to define the criterion. The language for stating the result is the same. See the following examples:

• The students in the class can be classified according to whether they are Asian or not. [criterion]
• The students in the class can be classified into Asian and non-Asian. [result]

Finally, it may be necessary to sub-divide, that is, to divide something which has already been divided. In this case, use 'sub-divided' for the second classification, and 'further sub-divided' for the next. See this example:

• The students in the class can be classified according to gender. They can be sub-divided according to whether they are Asian or not. They can be further sub-divided according to age, into those who are below 25 years of age and those who are above 25.

According to this classification, we will end up with eight groups: Asian males under 25, Asian males over 25, non-Asian males under 25, etc. This is summarised in the following diagram.

Structure

There are two main ways to structure a classification essay. The first way, shown in the diagram below (left), is when a single criterion (or single way of categorising) is used, resulting in distinct categories. The purpose of this type of structure is to show understanding of the categories, or justify the method of classification, by giving the categories and describing their characteristics. Sometimes the categories may be sub-divided into sub-categories, which may be listed or described. For the single-criterion classification essay, the criterion (if there is one) should be given in the general background of the introduction, and the thesis statement should list the categories which will be described in the main body. Each body paragraph will usually describe one category in detail.

The second way, shown in the diagram below (right), is when multiple criteria are used to classify the topic in different ways. The purpose of this type of classification is to show understanding of how the topic can be categorised, or justify the criteria for classification, by giving the criteria and showing examples of groupings using these criteria. For the multiple-criteria classification essay, the thesis statement should list the criteria which are described in the main body. Each body paragraph will usually describe the criteria and the groups it leads to. Depending on the level of detail, the examples might be broken down into separate paragraphs.

The two types of structure are shown in the diagram below.