Most people should be familiar with the concept of a proper noun, referring to the specific name of a person, place or thing. A proper noun would always be capitalized: Shakespeare, Los Angeles, Honda, etc. In this same manner, a proper noun can be converted into a proper adjective in order to describe another common noun. A proper adjective, such as Japanese or Canadian would also be capitalized, since it was formed from a proper noun such as Japan or Canada.
One of the reasons a writer may choose to use a proper adjective is a strong association between the proper noun and the description at hand. Because many of William Shakespeare's plays end tragically, it would not be unusual to describe a real-life tragedy of Shakespearean proportions. The adjective "Shakespearean" gives the reader a stronger sense of tragedy than using a common adjective such as "epic" or "serious" might provide.
Other proper adjectives used in this manner would include "Machiavellian," "Orwellian," "Pavlovian," or "Freudian." A ruthless politician might be described as a Machiavellian genius, for example, while an intrusive governmental policy could be seen as Orwellian. Because the proper adjective is formed from a proper name, such as Pavlov or Freud, it is also capitalized.
Another example of this kind of adjective involves the names of countries or cultures. A person may own a Japanese doll, make a German chocolate cake or order Canadian bacon for breakfast. These would all be considered proper adjectives, since they are derived from the proper names of countries. A writer may also refer to Arabian customs or Christian rituals, since those adjectives were formed from proper nouns.
Many times this type of adjective can be formed by adding certain suffixes to existing proper nouns. The use of the suffix -esque is commonly used to convert a proper noun into a proper adjective. A songwriter's new composition may be described as Dylanesque, for example, meaning that the song is reminiscent of singer/songwriter Bob Dylan's work. This tactic can also be used to create unique proper adjectives, such as describing a particularly difficult military situation as Vietnamesque or a political crisis as Nixonesque. Because the proper noun (Vietnam, Nixon) is closely associated with the subject matter, the proper adjective is effective.
Other proper nouns can be converted to proper adjectives by applying various suffixes such as -like, -ian or -istic. A conservative minister may hold a Calvinistic view on an issue, for example. A dictatorial boss may be described as Hitlerian, or a promising young political candidate may display Kennedy-like qualities.