Most outlines for a written work are categorized based on the way in which information is presented within them, including how much is indicated and how it is organized. A topic outline, for example, uses only short phrases or single words to present the general subject that will be explored in each section. In contrast to this, a sentence outline uses complete sentences to describe each topic, providing a great deal of information. Both of these types of outlines can be organized according to alphanumeric methods, in which letters and numbers are used to indicate different sections, or decimal systems that use numbers to differentiate between each subject.
Topic outlines are some of the most common formats, and use brief information to let a writer lay out the general structure of a written work. The basic format of such an outline is quite simple, consisting of one entry for each major point in the work, which often represents a paragraph or two. Within this are several sub-topics that are created to provide information that supports the major point, and this is repeated for each section of the work. Topic outlines only use a word or a short phrase to provide information about each point, which the author then expands upon in the writing.
In contrast to this, sentence outlines use complete sentences to provide the framework and information about a piece of writing. They are typically organized in much the same way, with subjects and sub-topics, but sentences are used instead of phrases. Such outlines can be quite convenient for work among multiple writers, as it allows them to better understand what each topic covers in more detail. Teachers who require an outline to be turned in with a paper may prefer the sentence type as well, since it allows them to better understand the subject the writer intended to cover in each section.
Both topic and sentence outlines are often structured in an alphanumeric method, which means they commonly use both letters and numbers. The first topic might be labeled as "1" with the sub-topics labeled "A," "B," and "C." Subjects within these might use Roman numerals, such as "i" and "ii," or lower case letters like "a" and "b." The next main topic would be "2," then "3" and so on.
Outlines can also be organized in decimal notation, which uses only numbers and no letters. The first subject can be labeled as "1.00," with the sub-topic as "1.10," then "1.20." Lower topics within this structure can then be "1.11," 1.12," 1.13," and so on. This type of organization works well for people who are naturally inclined toward mathematics, though some people are confused by the decimal notation.