 In the second half of the seventeenth century formal theory of probability is developed by researchers like Pascal (1623–1662), Fermat (1601 or 1606–1665) and Christiaan Huygens (1629–1695). The work De ratiociniis in ludo aleae of Huygens was translated in to English by John Arbuthnot (1692). For these authors, the world was essentially mechanistic and thus deterministic, probability was a quality of human knowledge caused by its imperfection: