Definition:Main Connective/Propositional Logic/Definition 2

Definition
Let $\mathbf C$ be a WFF of propositional logic such that:
 * $\mathbf C = \left({\mathbf A \circ \mathbf B}\right)$

where both $\mathbf A$ and $\mathbf B$ are both WFFs and $\circ$ is a binary connective.

Then $\circ$ is the main connective of $\mathbf C$.

Alternatively, let $\mathbf A$ be a WFF of propositional logic such that:
 * $\mathbf A = \neg \mathbf B$

where $\mathbf B$ is a WFF.

Then $\neg$ is the main connective of $\mathbf A$.

Also see

 * Equivalence of Definitions of Main Connective