Historians of Newton's thought have been wide ranging in their assessment of his conception of the trinity. David Brewster, in his The Life of Sir Isaac Newton (1831), was fully convinced that Newton was an orthodox trinitarian, although he recognized that "a traditionary belief has long prevailed that Newton was an Arian."1 Two reasons were used to defend his conclusion that Newton was orthodox. The first was a letter from John Craig, a friend of Newton, written shortly after Newton's death to John Conduitt, the husband of Newton's niece. In this letter Craig remarked that Newton's theological opinions "were sometimes different from those which are commonly received" but that he hoped Conduitt would publish Newton's theological papers, "that the world may see that Sir Isaac Newton was as good a Christian as he was a mathematician and philosopher."2 The second reason with which Brewster defended his conclusion was his acknowledgment that the doctrine of the trinity itself had variations.
I had no hesitation when writing the Life of Sir Isaac Newton in 1830, in coming to the conclusion that he was a believer in the Trinity; and in giving this opinion on the creed of so great a man, and so indefatigable a student of scripture, I was well aware that there are various forms of Trinitarian truth, and various modes of expressing it, which have been received as orthodox in the purest societies of the Christian Church.3
L. T. More in his biography Isaac Newton gently chided Brewster for not publishing some of the crucial manuscripts, which eventually became [End Page 57] part of the Keynes collection.4 From these additional manuscripts More reached the conclusion that Newton was not orthodox but an Arian. He proceeded to say that Newton was not only an Arian but, because of the manner in which he understood Jesus' role as prophet, a Unitarian.5
More recently the famous British economist John M. Keynes, who considered it a great "impiety" that the Portsmouth family's collection of Newton's non-scientific manuscripts were dispersed at the Sotheby's auction in 1936 and who recovered about half of them creating the "Keynes" collection at Cambridge, provided yet a third interpretation of Newton's thought.
Very early in life Newton abandoned orthodox belief in the Trinity. At this time the Socinians were an important Arian sect amongst intellectual circles. It may be that Newton fell under Socinian influences, but I think not. He was rather a Judaic monotheist of the school of Maimonides. He arrived at this conclusion, not on so-to-speak rational or skeptical grounds, but entirely on the interpretation of ancient authority. He was persuaded that the revealed documents give no support to the Trinitarian doctrines which were due to late falsifications. The revealed God was one God.6
Among contemporary scholars, the consensus is that Newton was an Arian rather than a Socinian.7 This view is clearly expressed by Richard [End Page 58] Westfall who writes, "Well before 1675, Newton had become an Arian in the original sense of the term. He recognized Christ as a divine mediator between God and man, who was subordinate to the Father who created him."8 Yet Frank Manuel, in his The Religion of Isaac Newton (1974), advises that we not try to push Newton into a theological categorization too quickly. He reminds us that Newton was, if nothing else, an original thinker.
It is an error to seize upon his antitrinitrianism in order to pigeonhole him in one of the recognized categories of heresy—Arian, Socinian, Unitarian, or Deist.9
So how did Isaac Newton conceive of the trinity? In exploring his writing on the subject we will be guided by two principles mentioned above. The first is Brewster's insight that the trinitarian doctrine has in fact been understood with a certain degree of variety within the sphere of orthodoxy. The second is from Manuel's reminder, that we must resist the temptation to make Newton "fit" some predetermined category or school of trinitarian thought. We will begin by looking at the resources available for studying...