Transition words and phrases are vital devices for essays, papers or other literary compositions. They improve the connections and transitions between sentences and paragraphs. They thus give the text a logical organization and structure.
All English transition words and phrases (sometimes also called 'conjunctive adverbs') do the same work as coordinating conjunctions: they connect two words, phrases or clauses together and thus the text is easier to read and the coherence is improved.
Usage: transition words are used with a special rule for punctuation: a semicolon or a period is used after the first 'sentence', and a comma is almost always used to set off the transition word from the second 'sentence'.
Example:
People use 43 muscles when they frown; however, they use only 28 muscles when they smile.
However, transition words can also be placed at the beginning of a new paragraph or sentence - not only to indicate a step forward in the reasoning, but also to relate the new material to the preceding thoughts. Use a semicolon to connect sentences, only if the group of words on either side of the semicolon is a complete sentence each (both must have a subject and a verb, and could thus stand alone as a complete thought).