Generally, common nouns, i.e., nouns that are generic, are not capitalized. A common noun is one that can be preceded by a or an and make sense in context:
a university a U. S. senator an engineer
EXCEPTION: The word President is always capitalized when it refers to any or all of the Presidents of the United States.
Common nouns that are separated from their proper nouns or names are occasionally capitalized. For example, titles of officials are capitalized when the titles replace the officials' names:
The report was submitted by the Treasurer. The Governor did not attend the meeting.
Similarly, names of close family members are capitalized when used in place of their proper name:
My concerns were for Mother, Father, and Aunt Millie. Don't forget, Father, that you promised to take me to the zoo.
When names of national divisions, government groups, and departments replace the entire name of those entities, they are capitalized:
The Department is aware of your concern. The bill was initiated in the House in the 1994 session. According to Accounting, the bill was paid last week.
Plural common nouns that follow two or more proper nouns are capitalized unless the common nouns denote topographical features:
the Treasury and Interior Departments Madison and Jefferson High Schoolsbutthe Atlantic and Pacific oceans the Columbia and Snake rivers