Here's why:
* Common nouns refer to general things or people, not specific individuals. Examples: dog, chair, city, teacher.
* Proper nouns name specific people, places, or things. They are always capitalized.
"Filipino" is a proper noun because it refers specifically to a person from the Philippines. It's similar to saying "American" or "Canadian."
Here's a quick way to remember:
* Common nouns are things you find in a dictionary.
* Proper nouns are things you find on a map or in a history book.