Compare these example sentences
- They talked to the president about the problem.
- They talked to President Joe Biden about the problem.
In Sentence 1, the word “president” is used as a common noun, so it is written in lowercase.
In Sentence 2, the word “president” is part of the name of the president; it is his title, so it is used as a proper noun and is capitalized.
- I gave my son an apple.
- I gave my son an Apple computer.
In Sentence 3, “apple” is used as a common noun. It is just an apple, so you write it in lowercase.
In Sentence 4, “Apple” is used as a proper noun. It refers to the name of a specific brand of computers, so you must capitalize it.
Example C. Compare how “mountains” is capitalized in these sentences:
- What are these montains called?
- They are called the Rocky Mountains.
In Sentence 5, “mountains” is a common noun, so it is not capitalized.
In Sentence 6, “Mountains” is a proper noun part of the name of the mountains (the Rocky Mountains), so it is capitalized.