The common noun simply identifies a person, place or thing in a common, general way without the need for capitalization. By contrast, proper nouns are used to identify a specific person, place or thing and usually do require a capital firs letter. For example, when referring to any "zoo" a common noun is used, but when referring to the "San Diego Zoo" a proper noun is used instead.
The chief distinguishing factor when identifying common nouns is how they describe something, someplace or someone. The common nouns "singer" or "president" become proper and capitalized when used more specifically as "Madonna" or "Barack Obama." A generic term like "dresser" is common as well until a brand name, such as "Broyhill®" is added.
Typically preceded by an article, such as "a," "an," "the," "this" or "that," a common noun can describe one person, place or thing as well as several at once. When a common noun has a grouping effect, it is called a collective noun. For example, this sentence shows a common noun that is also a collective noun: "The team won the game."
When a common noun is made up of more than one word, it is called a compound noun. "The fireman arrived at the house" uses a common compound noun. Other examples are "policeman," "chalkboard," and common nouns that can be two words, such as "ice cream" or "space station." These also are referred to as noun phrases.
The key distinction is that common nouns are generalized terms and proper nouns are specific. The capitalization aids the reader in making that distinction. Common nouns will not be capitalized unless they appear at the start of a sentence or as part of a title.
Common nouns also can be abstract or concrete, countable and uncountable. Abstract uses are needed to describe ideas or feelings, such as hatred or love. Concrete nouns that describe a seen-and-heard person or thing can be proper or common. "Paul needed to think of a better word," and "The student needed to think of a better word" both use concrete nouns, but the former sentence uses a proper form while the latter uses the common form. When grouped together, these nouns can either be countable or uncountable. In other words, common nouns like "student," "beans" and "chair" are quantifiable, but common nouns like "soil," "sunlight" and even "disgust" are considered uncountable because they cannot be accurately measured in total.