What are the differences between a perfect or pure monopoly a monopolistic competition oligopolies a perfect or pure competition?

Not many differences. Capitalism favors competition among private companies, but rarely creates monopolies. One source, in the references, says monopolies can be created by governments more than private companies.

References:
http://www.americansolvent.com/2009/07/03/competition-vs-monopoly-whats-the-big-confusion/