If the conclusion was fixed before the arguments were assembled, the arguments carry no evidence whatever the reader thinks of their quality.
Yudkowsky's device is a clerk who writes the verdict at the bottom of the page and then fills in the reasons above it. However good the reasons, the page's accuracy was determined when the bottom line was written, and reading the argument tells you nothing about the world. It is the sharpest available statement of why motivated reasoning cannot be corrected by better arguments.
In practice
- A report commissioned to support a decision already taken is not evidence for it, however rigorous.
- A researcher who knows which result would be publishable has written part of the bottom line already.