Consult Webster’s. If Webster’s says “often” or “mostly” or “usually,” capitalize. If it says “sometimes,” use discretion.
Hyphenated compounds in proper names or in titles: per Chicago 16 ed., capitalize the second element (e.g., "A Two-Thirds Majority of Non-English-Speaking Representatives"). See Chicago 8.161 for exceptions to this rule.
Brand names that begin with a lower-case letter: Retain the lower-case even when that name begins a sentence (e.g., "iPods are everywhere these days.")
The specialized vocabulary of a particular discipline may include words that are capitalized only in that discipline, e.g., Other or Scripture (Bible studies). If uncertain whether the capitalized form is generally accepted within that discipline, query the reviewer or someone else well qualified.
Capitalize the generally accepted names of historical periods and movements.
Capitalize the name of a specific art or architectural movement, group, or style (the Impressionism of Monet). Lowercase such a term when it is used in a general sense (John Manley’s paintings are impressionistic in manner). The prefix neo is lowercased unless specifically adopted by a group or movement as part of its name: the Neo-Impressionism of Seurat, but John Manley works in a neo-Dada manner.
CAPITALIZATION OF COMMON NAMES AND TERMS
Age of Reason
Civil Rights Movement
Colonial (18th-century US)
Enlightenment (18th-century philosophical movement)
Epistles (as section of Bible or specific reference, i.e., Epistle to the Romans)
fascism (general concept)
Fascism, Fascist Party (20th-century Italy)
fin de siècle
Gothic (only in context of art and architecture; lowercase in reference to novels or films)
Great Depression or the Depression
Great Society (aka Lyndon Johnson's Great Society)
left wing (n.)
Middle Ages; High Middle Ages; late Middle Ages; early Middle Ages
Native American, Native
New Criticism (context of literary criticism)
New South (1865 ff.)
the North (US)
Northern/Northerner (capped only in Civil War contexts)
Open Source Initiative
open source platform
Progressive Era (early-20th-century US movement)
Populism (late-18th-century political movement)
Reformation; Counter Reformation
Renaissance; High Renaissance
the Revolution (American)
right wing (n.)
Romanticism (18th-century movement)
war on terror
World Wide Web