In that sentence, 'cat' is the common noun and 'Mittens' is the proper noun because it is the specific name given to this one particular cat.

The word 'lake' names any body of water of that type in general. Because it is not a specific lake's name, it is a common noun.

'Tuesday' is the specific name of one day of the week. Days of the week are always proper nouns and start with a capital letter.

'Central Park' is the specific name of one famous park in New York City, so it is a proper noun. 'Park' alone would be common, but the full named form is proper.

The common noun that matches the proper noun 'Dr. Lee' is 'doctor.' 'Doctor' names any doctor in general; 'Dr. Lee' names one specific doctor.

The word 'store' names any store in general without pointing to a specific named store, so it is a common noun.

Proper nouns always begin with a capital letter. This distinguishes them visually from common nouns in a sentence.

In 'I love my dog Buddy,' the word 'dog' is the common noun (any dog) and 'Buddy' is the proper noun (one specific dog's name).

'Friday' is the proper noun name for one specific day of the week. The common noun category it belongs to is 'day.'

Each common noun is matched to its proper noun example: city → Chicago (a specific city), dog → Rex (a specific dog's name), teacher → Ms. Smith (a specific teacher's name), park → Central Park (a specific named park).