In Fall 2016, as a freshman, I presented a chapter from Feynman’s Lectures on Physics to freshman physics students at Sharif University. This was part of a series of weekly meetings organized by the student scientific organization. The chapter briefly discussed various interpretations of probability. As a freshman with limited experience, I found myself quite puzzled after reading it. How could we apply the same concept of probability, used in meteorology, to phenomena like radioactive decay?

Years later (in Winter 2020), after studying probability as a mathematical subject, I encountered Donald Gillies’s book, Philosophical Theories of Probability. This book offers a concise chronological overview of the philosophical interpretations of probability and provided some answers I had been seeking since that Feynman lecture. I believe this book is essential for anyone working with probability who is not a philosopher.

Gillies introduces the classical, subjective, frequency, and propensity theories of probability and concludes with a chapter on the intersubjective approach, which he himself developed. He argues that different philosophical interpretations of probability are employed—or should be employed—depending on the context, such as various scientific fields.