As noted earlier, subjects and predicates are related to nouns and verbs. Traditional grammar defines a noun as a person, place, or thing. However, this definition is not the best because it isn’t sufficiently inclusive. The word Monday, for example, is a noun, but it is not a thing, nor is freedom or any number of other words. For this reason, it is tempting to define a noun in terms of function:
A noun is any word that can function as a subject.