Transition words are essentially a mechanism used to alter the flow of text in context with the information provided. The use of transition words changes active text flow into a different functional context. This is sometimes referred to as altering the mindset of the flow of thought within a piece of text. A typical use of transition words is to go from a narrative state to use an example in context with the narrative. transition words may be used for illustration, contrast, addition of information,time, space, comparison,emphasis and details.

This is a series of transitional usages, in bold:

Road building is generally related to functional needs. For example, the Romans used roads specifically for military purposes while other civilizations used roads specifically for trade. It was suggested by historians that trade was one of the original primary reasons for the development of road systems. By comparison, Roman roads served clearly military purposes.