Proper Adjectives :
We took the northwest route during the spring thaw. We stayed there until the town's annual Fall Festival of Small Appliances.
When an adjective owes its origins to a proper noun, it should probably be capitalized. Thus we write about Christian music, French fries, the English Parliament, the Ming Dynasty, a Faulknerian style, Jeffersonian democracy. Some periods of time have taken on the status of proper adjectives: the Nixon era, a Renaissance/Romantic/Victorian poet (but a contemporary novelist and medieval writer). Directional and seasonal adjectives are not capitalized unless they're part of a title:
English Glossary Index
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