In his lifetime Boulton was likely better noted for his membership in the eclectic Metaphysical Society, a short-lived association (1869–1880) of some of Britain's most gifted philosophers, theologians, academics and political leaders, although "[n]o member of the Metaphysical Society knew less renown than M.P.W. Boulton". He was elected to the society in 1874. Nevertheless, the former and future British Prime Minister and society member William Gladstone, who chaired its 9 April 1878 meeting at the Grosvenor Hotel, read Boulton's philosophical treatise Has a Metaphysical Society Any Raison d'être? (Does a metaphysical society have any reason to exist?) to the assembled membership that evening. It included, in part:
