  In this pedagogical text aimed at those wanting to start thinking about or
brush up on probabilistic inference, I review the rules by which probability
distribution functions can (and cannot) be combined. I connect these rules to
the operations performed in probabilistic data analysis. Dimensional analysis
is emphasized as a valuable tool for helping to construct non-wrong
probabilistic statements. The applications of probability calculus in
constructing likelihoods, marginalized likelihoods, posterior probabilities,
and posterior predictions are all discussed.
