\begin{definition}[Definition:Propositional Function]
A '''propositional function''' $\map P {x_1, x_2, \ldots}$ is an operation which acts on the objects denoted by the object variables $x_1, x_2, \ldots$ in a particular universe to return a truth value which depends on:
:$(1): \quad$ The values of $x_1, x_2, \ldots$
:$(2): \quad$ The nature of $P$.
\end{definition}