At first glance, the rules of English capitalization seem simple. You probably know you should capitalize proper nouns and the first word of every sentence. But you also (sometimes) capitalize the first word of a quote. Usually you don’t capitalize after a colon, but there are exceptions. And what do you do when you’re not sure whether something is a proper noun?
English Capitalization Rules:
1 Capitalize the First Word of a Sentence
This one’s easy. Always capitalize the first word of a sentence.
2 Capitalize Names and Other Proper Nouns
You should always capitalize people’s names.
Names are proper nouns. The names of cities, countries, companies, religions, and political parties are also proper nouns, so you should capitalize them, too.
You should also capitalize words like mom and grandpa when they are used as a form of address.
3 Don’t Capitalize After a Colon (Usually)
In most cases, you don’t need to capitalize after a colon.
There are a couple of common exceptions. One is when the word following the colon is a proper noun.
The other exception is when the words following the colon form one or more complete sentences.
4 Capitalize the First Word of a Quote (Sometimes)
Capitalize the first word of a quote when the quote is a complete sentence.
Don’t capitalize the first word of partial quotes.
5 Capitalize Days, Months, and Holidays, But Not Seasons
The names of days, months, and holidays are proper nouns, so you should capitalize them.
The names of seasons, however, are not proper nouns, so there’s no need to capitalize them.
6 Capitalize Most Words in Titles
The capitalization rules for titles of books, movies, and other works vary a little between style guides. In general, you should capitalize the first word, all nouns, all verbs (even short ones, like is), all adjectives, and all proper nouns. That means you should lowercase articles, conjunctions, and prepositions—however, some style guides say to capitalize conjunctions and prepositions that are longer than five letters.
7 Capitalize Cities, Countries, Nationalities, and Languages
The names of cities, countries, nationalities, and languages are proper nouns, so you should capitalize them.
8 Capitalize Time Periods and Events (Sometimes)
Specific periods, eras, and historical events that have proper names should be capitalized.
However, centuries—and the numbers before them—are not capitalized.
from Grammarly Blog https://www.grammarly.com/blog/capitalization-rules/