Note: With all the types of rhetorical strategy mentioned below, we are not talking about essay "types", but about rhetorical styles which writers use for particular purposes. Some essays ask for a more expository than argumentative style, and for particular strategies within those styles. As we shall see later, authentic essays actually require you to use a combination of these styles.

Expository (mainly):
"Exposition" is a rather formal term which really means either "information" or "explanation", modes of communication we might use to write a manual, offer instructions on how things work or  where to find things, or recount what happened during a revolution, etc.
Below we have identified 4 types of expository essay found in university curricula: 

Descriptive
Science-related essays often require background description: of a thing, process or state of affairs - analyzing it into its parts. This can be done chronologically, serially, hierarchically, etc. It is a test of your ability to select and synthesise ‘factual’ information.

Explanatory
This approach is asked for in essay looking for an account of reasons or causes in relation to perceived effects or results. In most Social Science disciplines, you will be asked to draw on theory to support your explanation. Your interpretation demonstrates how well you understand the relevant theories.

Illustrative
This could be fairly descriptive, but illustrations need to be relevant and appropriate, and written with explicit reference to the theoretical point being supported.

Analytical
This could apply to experimental data, or to an argument or text. It is the process of breaking down something into its component parts, often in order to analyse patterns or categories based on a theoretical position.

Argumentative (mainly)
Argumentative literally refers to everything that involves debate and possible disagreement, and to opinion as opposed to the uncontested facts of exposition. It means agreeing or disagreeing with a given proposition, either strongly or tentatively.

In more general terms it refers to a more subjective style of writing, where writers engage in defining their terms or interpreting and evaluating the views, evidence or data very clearly from their own perspective or viewpoint.

Defining
Essays which expect a strong defining component are common in philosophy, but also feature in Sociology.
A question may look factual- e.g. ‘Do we have free will?’ , but the way to answered it is by careful definition of what is meant by the concept of free will.

In Sociology, in particular, competing definitions often need to be explored at length, particularly in essays on social stratification or social class.

Evaluative Some essays require you to pass judgement or make an assessment, according to stated criteria. In cases when you could say ‘Well, it depends what you mean by (X) ... ’, it is important that you define the terms by which you apply or explore these criteria. Terms, such as "success" or "effectiveness", are often value-laden.. Basically, you may be asked to judge how good or bad something is, or how far it is true. E.g.: Evaluate the contribution of political parties to the development of

the movement for democracy in Hong Kong

Interpretive Interpretation is classically a literary process, where you place your interpretation of a text in the context of other, perhaps more established interpretations. It is also often used in Political Science and History, where
•	the causes, developments and results of political developments or events are interpreted,
•	there are conventional (and often competing) interpretations to re-examine

Note: Interpretation + Evaluation: Critical Review Essays typically combine these processes and styles of writing 

In all argumentative essays, you are expected to
•	consider all sides of an issue before taking a stand, and then to
•	argue for the validity of your own position