Nouns referring to non-specific people, places, and things are called common nouns. Common nouns only begin with a capital letter if they are the first word of a sentence.
The dog barked excitedly when he heard company arriving outside.
The noun dog is a common noun because it does not refer to a specific dog. It is simply a vague reference to a dog. It could refer to any dog in the world because it is not specific.
Beth’s little brother was very annoying sometimes.
Brother is a common noun here because it is not specifically naming a person. Although the context of the sentence does narrow things down, the noun brother in and of itself is very vague.
We went on a tour of a historical site.
The site mentioned here is another common noun because it does not name a specific place. Regardless of context, the noun site on its own does not indicate a specific place.
The Johnsons’ eldest son is an engineer.
In this example we see again that context and other information given in the sentence are irrelevant when deciding whether a noun is common or proper. Obviously, there can be only one eldest son in the Johnson family, but son is still not specific in and of itself.
The president will be giving a speech this evening.
Words like president and others that refer to specific positions of authority are often tricky for some people, but it is important to remember that the title itself does not identify a specific person. On its own president is just a title and does not name a particular person.
My mom is making pie today.
Similar to president in the previous example, family titles are common nouns unless they are being used to refer to someone by the title itself or as nouns of direct address.
Nouns referring to specific people, places, and things are called proper nouns. Proper nouns almost always begin with a capital letter.
Fido wagged his tail uncontrollably when our visitors came inside.
The noun Fido is proper because it refers to a specific dog by name. It is not vague or generic like the common noun dog.
Beth’s friends were appalled by how much of a nuisance Freddy could be.
The noun Freddy is proper because it names a specific person. While common nouns like person or brother could refer to all kinds of people, Freddy identifies a particular person.
Our class went on a field trip to the Lincoln Memorial.
Lincoln Memorial is a proper noun because it names a specific place. The noun site in a previous example could refer to any number of places, but Lincoln Memorial is highly specific.
Ted Johnson is a highly qualified electrical engineer.
The specific name Ted Johnson is a proper noun. It identifies the Johnson’s eldest son by name.
President Washington set a noble standard for all future presidents to follow.
In this case, president is not just referring to the position or title in general. It here refers to a specific president by name.
Mom and Dad got my brother a new bike.
Family titles identifying or addressing specific people in place of their names are proper nouns. Here the speaker is not referring generally to the parental roles of his mom and dad. He is specifically identifying the individuals as Mom and Dad, using their titles in place of their names.
Thank you for your help, Pastor.
As with Mom and Dad in the previous example, when we identify or address someone by their title only, the title is a proper noun. In this sentence, Pastor is not referring to a pastor. It is addressing a specific individual.
Matt got a new iPhone last week.
Specific brand name items and companies are proper nouns. A generic term like phone or cellphone is common, but iPhone is a proper noun referring to a specific brand of phone. Words like iPhone are the reason I said that proper nouns almost always begin with a capital letter. Even if a company or brand’s official name begins with a lower-case letter, the name is still a proper noun.