Proper nouns are specific names of people, places, or things (e.g., John, London, the Eiffel Tower).
Common nouns are general names for people, places, or things (e.g., man, city, tower).
Here are some examples of sentences without proper nouns:
* The cat sat on the mat. (All common nouns)
* She went to the store. (All common nouns)
* It is raining outside. (All common nouns)
You only need a proper noun if the sentence refers to a specific individual, place, or thing.