Common - proper noun
A noun may be either a proper noun or a common noun.
A proper noun is a noun which refers uniquely to a particular individual of a specific kind, whether a person, an animal, an object, a place, an idea, or whatever, as in, e.g., ‘John Smith has bought a new car’, ‘We took Tabitha (our cat) to be examined by the vet’, ‘Everest is the highest mountain in the world’, ’Berlin is the capital of Germany’, and ‘The Renaissance began in Italy in the fourteenth century’. Note in connection with the first of these examples that while the name ‘John Smith’ is common to very many individuals, when it is used on any particular occasion, it refers to a particular individual – which one will be known to the speaker and the person(s) to whom he or she is speaking. As will be apparent from these examples the clearest instances of proper nouns are names – indeed proper nouns are sometimes called proper names or simply names. As such, proper nouns are almost always written with an initial capital.
A common noun is a noun which is used to refer to any member, or some, or all of the members of a particular class, whether of persons, animals, objects, places, etc., as in, e.g., ‘A dog can make a good pet’, ‘It is wrong to keep lions in captivity’, ‘Fresh fruit is an essential element in a healthy diet’, ‘All men are mortal’, ‘The more experienced members in the group led the way into the cave’. As will be clear from the examples in this and the preceding paragraph, common nouns are often used with the definite or indefinite article, while proper nouns are not usually so used - though for some exceptions see Eponyms A-M and Eponyms N-Z.