Let $P = (\Omega, \mathcal{F}, \mathbb{P})$ be a D1159: Probability space such that

(i)	$E, F \in \mathcal{F}$ are each an D1716: Event in $P$
(ii)	\begin{equation} \mathbb{P}(F) \in (0, 1) \end{equation}

Then \begin{equation} \mathbb{P}(E) = \mathbb{P}(E \mid F) \mathbb{P}(F) + \mathbb{P}(E \mid F^{\complement}) \mathbb{P}(F^{\complement}) \end{equation}