Philosophical Necessity influenced the 19th-century utilitarians John Stuart Mill and Herbert Spencer, who were drawn to its determinism.
The philosopher A. Spir believed that the work had so clearly refuted the notion of free will, that it is unnecessary to discuss the issue anymore. In a similar fashion, Arthur Schopenhauer commented that "no writer has presented the necessity of acts of will so thoroughly and convincingly as Priestley ... If anyone is not convinced by this supremely clearly and accessibly written book, his understanding must really be paralysed by prejudices", and that the work contributed to Kant taking the complete necessity of acts of will as a settled matter to which no further doubt could pertain.
This was apparently from Schopenhauer’s book called On the Freedom of the Will, but I can’t find the book or anything from Kant.
What did Kant think about The Doctrine of Philosophical Necessity, or if nothing can be found, what did Kant think about the philosophy of Joseph Priestley in general?
You can read The Doctrine of Philosophical Necessity, and practically everything from Priestley, online for free. He’s not well known today, but he was VERY popular during the Enlightenment.