I know that: $$P(c|o) = \frac{P(o|c) P(c)}{P(o)}$$
My question is why can't one calculate $P(c|o)$ directly and not use this formula?
I know that: $$P(c|o) = \frac{P(o|c) P(c)}{P(o)}$$
My question is why can't one calculate $P(c|o)$ directly and not use this formula?