https://maximummathematics.com/books/foundational-mathematics/logic/open-propositions/index.htmlAll of the propositions we’ve dealt with so far have had definite truth values. For example, $$\text{Thomas Jefferson was the second president of the United States.}$$is a proposition that is known to be false. A statement such as $$\text{2 + 2 = 4, or 2 + 2 = 5.}$$is a compound proposition that is true. However, a statement such as $$\text{$n$ is 1 more than a multiple of 3.}$$is not a proposition, because we don’t know whether it’s true or false. We would need to know the value of $n$ in order to reach such a conclusion. For example, the statement is false when $n = 5$, but true when $n = 16$. Here, we’ll deal with sentences involving variables like this one.Hugoen-US