It’s not that no given evidence should change your confidence level (that would mean that you do not update your beliefs in response to evidence, which is contrary to rationalism), but that your expected post-evidence confidence level should be the same as your pre-evidence confidence level.
Note that the word “expected” here is a technical term in probability theory and statistics that does not always match up with natural-language uses of the term. What I mean by “expected post-evidence confidence” here is “the weighted mean posterior probability”.
Of course, once you see the evidence, your confidence level should change, and you should always expect that to happen. That’s the definition of evidence; an event that will change your confidence level.
If you still don’t understand the difference, learn probability theory notation to be able to read the formulas provided in the text.
It’s not that no given evidence should change your confidence level (that would mean that you do not update your beliefs in response to evidence, which is contrary to rationalism), but that your expected post-evidence confidence level should be the same as your pre-evidence confidence level.
Note that the word “expected” here is a technical term in probability theory and statistics that does not always match up with natural-language uses of the term. What I mean by “expected post-evidence confidence” here is “the weighted mean posterior probability”.
Of course, once you see the evidence, your confidence level should change, and you should always expect that to happen. That’s the definition of evidence; an event that will change your confidence level.
If you still don’t understand the difference, learn probability theory notation to be able to read the formulas provided in the text.