# Popper’s Laws of the Excess of the Probability of the Conditional over the Conditional Probability

*Conceptus: Zeitschrift Fur Philosophie*26:3–61 (1992/93)

**Abstract**

Karl Popper discovered in 1938 that the unconditional probability of a conditional of the form ‘If A, then B’ normally exceeds the conditional probability of B given A, provided that ‘If A, then B’ is taken to mean the same as ‘Not (A and not B)’. So it was clear (but presumably only to him at that time) that the conditional probability of B given A cannot be reduced to the unconditional probability of the material conditional ‘If A, then B’. I describe how this insight was developed in Popper’s writings and I add to this historical study a logical one, in which I compare laws of excess in Kolmogorov probability theory with laws of excess in Popper probability theory.

**Keywords**

**Categories**

(categorize this paper)

**PhilPapers/Archive ID**

DORPLO

**Upload history**

Archival date: 2013-11-09

View other versions

View other versions

**Added to PP index**

2013-11-09

**Total views**

372 ( #16,035 of 2,433,543 )

**Recent downloads (6 months)**

23 ( #30,926 of 2,433,543 )

How can I increase my downloads?

**Downloads since first upload**

*This graph includes both downloads from PhilArchive and clicks on external links on PhilPapers.*