  Along these lines, it has been proposed that the logical constants are just those expressions that can be characterized by a set of purely inferential introduction and elimination  rules.[20]  To grasp the meaning of the conjunction connective \(\dq{\and}\), for example, it is arguably sufficient to learn that it is governed by the rules:  \begin{equation*} \frac{A, B}{A \and B} \quad \frac{A \and B}{A} \quad \frac{A \and B}{B} \end{equation*}  Thus the meaning of \(\dq{\and}\) can be grasped by anyone who understands the significance of the horizontal line in an inference rule. (Contrast \(\dq{\%}\) from the last section, which cannot be grasped by anyone who does not understand what a male is and what a widow is.) Anyone who is capable of articulate thought or reasoning at all should be able to understand these inference rules, and should therefore be in a position to grasp the meaning of \(\dq{\and}\). Or so the thought  goes.[21]