Conditional Probability
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In Probability,
In the real world, probabilities are not straightforward, like $P \rightarrow Q$. Therefore we translate into $P(B|A) \approx 1$. If $A$ happens, then B is most likely to happen. This defines as
$$ P(B|A) = {P(A \cap B) \over P(A)} $$
This means
$$ {P(A \cap B)} = P(B|A) P(A) $$
$P(B|A)$ is the likelihood and $P(A)$ is the prior.