Threat of debtors' prison sharpened Dunckerley's imagination tremendously. Still, passing himself off as a royal bastard seems an unlikely and outrageous strategy, with very uncertain results. Thus the temptation for us to look into Dunckerley's past for clues about his mindset is irresistible. What could he have been thinking? Fortunately, amongst his fairly slender literary remains, he does leave a clue. In 1750, Thomas Dunckerley was a member of the Sober Society of Portsmouth Common, in Hampshire. The society took as its motto ‘Virtus tandem Viegbit’ or, as Dunckerley himself notes in a lecture, ‘Virtue at length shall flourish’. The society was active from at least 1747 to 1754, though it left only scattered traces in the historical literature. The earliest mention of the society appears in a bound manuscript dated 3 April 1747, which was described in the Journal of the Ex Libris Society in 1894. Unfortunately the location of this manuscript is unknown and its survival uncertain. However, Dunckerley's own manuscript notebook of lectures survives at the Lady Lever Art Gallery at Port Sunlight, outside Liverpool.

The structure and content of Dunckerley's writing tells us a good deal about the society. The notebook contains thirteen motivational lectures, dated between December 1749 and December 1750.