Pm.sample() - How can the posterior be defined when there is no observed data to calculate the likelihood?

Questions
9

Thanks @ricardoV94 for the explanation. I have a follow-up question on the same.

Sometimes, but not always. If there are transforms that distort the prior like ordered or sumto1 in a variable, pm.sample will provide different (and correct) draws from the prior whereas prior predictive won’t.

Could you help me understand how ordered and sumto1 transformation would distort the prior when using pm.sample() and not when using pm.sample_prior_predictive()? An example would help.