And so Flew grew to be a leading philosopher of the school of evidentialism, endlessly strictly demanding that belief ought to follow the evidence, and ruthlessly weeding out claims of faith which were not founded on insurmountable logic (which, for the most part, discounted all forms of faith for him). Flew's primary position was that atheism ought to be presupposed until testable, empirical evidence of a God (or comparable metaphysical entity) should arise -- he rejected out of hand the notion of any God which could or would make itself untestable, characterizing such propositions as simply meaningless. Likely his most famous contribution to philosophical dialogue was the no true Scotsman fallacy, a proposition that focused some light on the problem of dissenting voices within a group being characterised by their opponents as simply not being members of the group.
But late in life, Flew's discernment of where the evidence led caused him to undertake a rejection of atheism itself, in favor of the position of Deism. An elderly Flew wrote -- with the assistance of another philosopher, Roy Abraham Varghese -- a book confrontationally titled There Is A God. The clincher for Flew was the plethora of fortuitous circumstances in our Universe, from constants of physics to the peculiar dual dance of DNA and RNA which Flew saw as a form of code requiring, at least obliquely, a code-writer. Flew's death not long after caused 'followers' in three camps to advocate for specific aspects of his work.
Atheists who had long rallied behind Flew's actively and eloquently antitheistic writings insisted that Flew's late-life conversion had been brought about by confusion and deception as to what science could answer about the origin of life; it was hinted without subtlety that senility had played a role (and, indeed, this argument was made even while Flew still lived). Some proposed that Flew had experienced something of a death-bed conversion brought about by fear of afterlife consequences, a proposition Flew flatly scotched with the assurance that despite coming to believe in a designer, he continued steadfastly rejecting the notion of an afterlife. But most of all, the atheists sought to dismiss Flew's late-life deistic turn as an anomalous period in the life of a tried-and-true atheist whose great bulk of work was uncompromisingly atheistic. The work, they contended, spoke for itself, and itself overpowered the arguments upon which Flew later came to rest.
Theists, on the opposite tack, sought to extend Flew's views into territory which Flew himself expressly continued rejecting, begging the possibility that Flew's ascent to Deism placed him on the path to accepting some brand of Theism, much as a man who walks up from a valley to the top of a mountain before dying might afterwards be described as having been on a path to walk right on up to the moon. To read obituaries produced by some theistic publications would be to conclude that Flew had indeed approached becoming a deity-worshiping believer in literal theistic scripture, replete with an angry, jealous, haphazardly intervening Creator, and stone-age creation myth. Such representations optimistically ignored that Flew's views had actually become even more hardened against theistic contentions as he entered into the realm of deistic thought. To Flew, the very possibility of a noninterfering deistic God rendered unnecessary and absurd the claims of the bother of a theistic tinkerer-deity. In 2006 an evangelical university had given Flew an award for his freedom of thought (presumably for shifting from atheism to Deism), though Flew himself had not wavered from what he'd announced in a 2004 interview:
I'm thinking of a God very different from the God of the Christian and far and away from the God of Islam, because both are depicted as omnipotent Oriental despots, cosmic Saddam Husseins.
Flew, rather, compared his Deism to the position of Thomas Jefferson, declaring:
While reason, mainly in the form of arguments to design, assures us that there is a God, there is no room either for any supernatural revelation of that God or for any transactions between that God and individual human beings.
And, at last, there were the deists (including pandeists), the small but enduring group of adherents to the position to which Flew ultimately did hew, declaring himself to be "quite happy to believe in an inoffensive inactive god." As followers of precisely this view, they defended Flew's final writings on the contention that these ought to be taken for the value of what they set forth, without consideration of the author's life external to his work. The deist, then, was tasked with combating barbs hurled both from the side of the atheists who dismissed Flew's post-atheistic writings on the grounds of deceived and diminished faculties; and from the theists who misrepresented Flew's end-of-life philosophical evolution as endorsing their view. In a sense, deists were tasked still with countering Flew himself, for though his potent antitheistic arguments were most squarely directed against theistic beliefs, elements of them could be read as antideistic and antipandeistic as well. There are indeed legitimate questions raised as to whether Flew did truly fully grasp the science of genetics which played a large part in his late conversion, and indeed it is hardly an article of faith amongst deists that the code of life requires a direct author at all, if a Universe might be designed which authors such things incidentally. But further back from that, the notion of authorship may not be withdrawn, for Deism fathoms the ability of a Universe itself to give rise to such a complex code as evidence of a complex design.
But whatever else may come from the late-life conversion of Antony Flew, it surely succeeded in drawing new attention both to his antitheistic life's work, and to the deistic ideas which were his final ideological resting place.