Archive for December 4, 2015

Bayes’ Theorem or Price’s Theorem?

Posted in History, The Universe and Stuff with tags , on December 4, 2015 by telescoper


I’m indebted to a fellow blogger for drawing my attention to the person shown in the above picture, Dr Richard Price who has been described as “the most original thinker ever born in Wales”, and who has a Society named after him.

Price was a moral philosopher, nonconformist preacher and also a mathematician of some note. Of particular interest to this blog is the role he played in the development of what is now known as Bayes’ Theorem, after the Reverend Thomas Bayes.

However, the paper in the Philosophical Transactions of the Royal Society that contains the first published form of this theorem was not published until 1763, over a year after Bayes’ death and, as you can see if you follow the link, is attributed jointly to “Mr Bayes and Mr Price”.  It appears that there was an original manuscript written by Bayes around about 1755  which was communicated to Price when Bayes died in 1761 and then presented for publication over a year later; Price had been asked to act as “literary executor” of Bayes’ estate.

Unfortunately the original manuscript has never been found and it is therefore impossible to say for sure how much Price contributed to the final version. However, a relatively recent and very interesting article  raises this question, and argues (reasonably convincingly to my mind) that Bayes’ part stops at page 14 of 32 pages. It is therefore quite possible that Price wrote over half the paper himself although most historical discussions of this matter simple state that Price “edited” Bayes’ work.

It has to be said that the paper is not exactly a model of clarity and pertains only to a particular case of the full theorem. The form in general use today was first published by Laplace in 1812, so it should really be called Laplace’s Theorem, but Laplace did give generous credit to the work of Bayes which is no doubt why the name stuck.

I don’t suppose we will know for sure exactly how much Price contributed to the development of Bayes’ theorem, but this may be yet another example of the law that any result in science or mathematics that has a person’s name attached to it has the wrong name attached to it!

Finally, I will mention that the Richard Price Society has started a petition to the Welsh government. I’m taking the liberty of copying the purpose of this petition here:

We call on the Welsh government to acknowledge the important contribution of Dr Richard Price not only to the eighteenth century Enlightenment, but also to the making of the modern world that we live in today, and develop his birthplace and childhood home into a visitor information centre where people of all nationalities and ages can discover how his significant contributions to theology, mathematics and philosophy have shaped the modern world.

Tynton Farm in Llangeinor, the birthplace and childhood home of Dr Richard Price is for sale. Once derelict, the farm has been sensitively restored and almost all of the original features have been preserved. The Richard Price Society is aware that the house attracts visitors from all corners of the globe and this is attested by the previous owner’s Visitors Book that was signed by visitors to the farm. The position of the farm and its provenance would make it an ideal learning centre where people can find out just what an important person he was and remains. This is an opportunity to buy the property at market value and help celebrate the achievements of Wales’ intellectual giant and apostle of liberty.


I have signed it, and hope you will consider doing likewise!