 Bolzano is not content with this concept of probability simpliciter but rather continues to develop an even more important relative concept of probability. What is at stake here is the probability of a proposition \(s\) relative to a set \(\sigma\) of propositions with respect to a sequence \(i\) of ideas, and in particular with respect to \(i^{\sigma \cup \{s\}}\), i.e., the sequence of all simple extra-logical ideas contained in \(s\) or \(\sigma\). Its degree can again be represented by a fractional number \(0 \le^m /_n \le 1\), where \(n\) is the number of cases where \(\sigma\) comes out true and \(m\) is the number of cases where \(\sigma \cup \{s\}\) comes out true (WL II, 171–191; for a careful reconstruction of Bolzano’s theory of probability see Berg 1962, 148–150).