While it's not the case in every language, in English we capitalize the days of the week and the months of the year. It doesn't matter if it's at the beginning, the middle, or the end of a sentence. Always use a capital letter at the beginning of days of the week and months of the year.
Incorrect: We went to the store on monday.
Correct: We went to the store on Monday.
Incorrect: My birthday is in june.
Correct: My birthday is in June.
Every language has different rules for capitalization. In English, we always capitalize the days of the week and the months of the year. There are no exceptions to this rule. Always capitalize the months and days, no matter where they are in your sentence.
Incorrect: On wednesdays, we wear pink.
Correct: On Wednesdays, we wear pink.
Incorrect: Do you want to go out on friday?
Correct: Do you want to go out on Friday?
Incorrect: She was born on thursday, november fifth.
Correct: She was born on Thursday, November fifth.
Incorrect: I clean the house every sunday.
Correct: I clean the house every Sunday.
Incorrect: december is my favorite month.
Correct: December is my favorite month.
