In college, you will be faced with a number of essay assignments. Whether you are writing a literary analysis, a chemistry report or a historical research project, you will find that for each type of essay, you must abide by certain guidelines. According to the Purdue Online Writing Lab, there are four genres of essays: description, narration, exposition and argumentation. Each of these essays, however, requires different guidelines.

Descriptive Essays

According to the Purdue Online Writing Lab, the descriptive genre allows "for a great deal of artistic freedom," in which a writer can paint vivid images with words. The central guideline for writing a descriptive essay is that the writer must choose his vocabulary carefully. For example, if you are asked to write a description about horseback riding, put the reader on a horse alongside you by describing everything about the experience. For instance, rather than writing, "Horseback riding is a fun activity," be more vivid. Assume the reader has never ridden a horse. How does it feel? What are your emotions? What are you thinking as you sit in the saddle? This will effectively evoke images in your reader's mind.

Narrative Essays

Like the descriptive essay, a narrative essay may also allow creative freedom in the form of storytelling. According to the Purdue Online Writing Lab, if written as a story, your narrative should include all elements of storytelling, such as an introduction, plot, characters, setting, climax and conclusion; however, a narrative essay does not always have to be written in the form of a story. For example, a book report may be more informative than creative; however, it should still ignite some emotions within the reader.

Expository Essays

An expository essay is intended to share information with the reader. The main focus of the information is introduced in the thesis statement, which usually appears in the first paragraph of the essay and lets the reader know what the paper is about. For example, if you are writing a research essay about the disadvantages of drinking diet soda, your thesis statement might read something like, "Although substituting diet soda for regular soft drinks may provide some health benefits, consuming diet soda also poses major risks to your health." This informs the reader that the rest of your paper is about the health disadvantages of drinking diet soda. You must then support this claim with reliable evidence. For instance, if your goal is to educate readers about the dangers of drinking diet soda, support these claims with credible sources, such as studies conducted by major universities. Finally, you need to conclude the essay in your own words. Do not repeat the thesis statement. Instead, bring your essay full circle by offering your own personal advice or opinion relevant to your thesis statement. Furthermore, you must list all references cited in your paper -- whether books, websites or surveys -- on a separate Works Cited or References page.

Persuasive Essays

In a persuasive essay, also known as an argumentative essay, you take a stand on a specific issue and attempt to persuade the reader to adopt your beliefs. Your persuasive essay should contain a thesis statement in the opening paragraph. For example, if you are trying to persuade the reader that a laptop computer is better than a desktop computer, your thesis statement might read, "The advantages of owning a laptop computer outweigh those of owning a desktop computer." You should then transition to the body of the essay, offering evidence and examples that support your argument. Some evidence might include interviews, surveys or credible studies, as long as the evidence remains relevant to your thesis statement. However, according to Austin Peay State University, it is also "unethical to exclude evidence that may not support the thesis." For instance, if there are some studies or positions that oppose your argument, you must also include these in your essay. Rather than writing about how you think these opposing positions are completely wrong, explain how perhaps the opposing position may be outdated or too generalized. Finally, conclude your paper. Rather than repeating your thesis statement, your conclusion should leave a lasting impression on the reader.