It is shown that probabilistic beliefs and est imation of quanti t ies give rise to the same model, that of a type spacer and can be viewed as the two sides of the same coin. We s tudy the axiom of correct est imation, which s ta tes tha t an agent 's est imation of his own est imation is correct, showing it to be weaker than the introspection axiom, according to which an agent is certain of hi...