I saw the word “credence” in a blog post by Sean Carroll. He defines credence as “degree of belief.” Here’s an interesting quote from that blog post
“Quantum probabilities are really credences — statements about the best degree of belief we can assign in conditions of uncertainty — rather than statements about truly stochastic dynamics or frequencies in the limit of an infinite number of outcomes. But these degrees of belief aren’t completely subjective in the conventional sense, either; there is a uniquely rational choice for how to assign them.”- Sean Carroll
In his “Probability in Philosophy” Brian Weatherson defines credence as “degree of confidence” and warns us that the other definition – “degree of belief” – is misleading. On the other hand, the authoritative SEP says: “Our beliefs come in degrees; we believe some more strongly than others. We call the strengths of our beliefs our credences“
I am not going to discuss Quantum Mechanics here. In Carroll’s post the part that attracted my attention was the conceptual difference between the “epistemic” and the “credence.”
As Carroll says, the term “epistemic” refers to statements about our knowledge of the world and not to the statements about the world itself. Normally the word “epistemic” is contrasted to the word “ontological.” The branch of philosophy known as ontology is interested in the knowledge of the real (truth). The other branch of philosophy known as epistemology tries to find answers to the questions “how do we know the truth?”, “what is knowledge?” and “how is knowledge acquired?”
The term “epistemic” belongs to epistemology. The word “ontological” belongs to ontology. What branch of philosophy does the term credence belong to? Not to philosophy, in my opinion!
It seems to me that the concept of “credence” belongs to the discipline of probability&statistics, more specifically to Bayesian statistics. The review article by Michael Strevens (NYU) titled “Notes on Bayesian Confirmation Theory” is a must-read. Michael Strevens defines “credence” as “subjective probability.”
Quantum Mechanical probability is a different type of probability. It is certainly different from the “frequentist interpretation” of probability, and it is also different from the “Bayesian interpretation” of probability. The Quantum Mechanical probability is designed to maximize prediction. This is a huge subject. I will comment on the Quantum Mechanical probability in the future.