One usually imagines a disagreement about the existence of demons to be a dispute between superstition and reason, between loyalty to authority and devotion to rational investigation. This was indeed the case with some rabbinic scholars. Figures such as R. Moshe Taku did not care for rational investigation; it was only received tradition that counted. At the other extreme, R. Yaakov b. Abba Mari Anatoli fully acknowledged that great Sages had believed in the existence of demons, but nevertheless was emphatic that they did not exist and lamented the errors of the greats.
Yet we see very little difference between some of those who believed in demons and some of those who denied their existence. Compare, for example, Chasdai Crescas and Levi b. Avraham. Both state that one should accept that which is a received tradition from prophets and Sages, and that which is experientially demonstrated. Crescas determines that demons are indeed a received tradition from prophets and Sages, and have been experientially demonstrated, whereas Levi considers that they have not been experientially demonstrated and are not a received tradition from prophets and Sages. Likewise, figures such as Ramban and Avraham Yagel justified their belief in such things on the grounds of (alleged) empirical evidence. In principle, the methodology is the same; the difference in application and results simply reflects a difference between the intellectual climates in which the different figures lived.
Or maybe not. It can be argued that while all proclaim the same methodology, in fact they are different. For Crescas (and much more so with non-philosophers) it is received tradition that is dominant, whereas for Levi it is experiential demonstrations which are dominant, with the traditions being (subconsciously re-)interpreted in light of this. After all, at the end of the day, most of the rationalist philosophers did not accept the existence of demons. The reason why their intellectual climate did not include them is precisely because their focus was on that which can be experientially demonstrated and intellectually comprehended.
Perhaps both ways of looking at it have are partially true. It is clear that some of the authorities who believed in demons, especially in the earlier period, were nevertheless at least in principle much closer to the rationalist approach than those in recent times and today who believe in their existence for solely traditionalist reasons. And even many people today who do not believe in demons are themselves far from rationalistically inclined; they simply accept the beliefs of the society in which they live. Ramban and Levi b. Avraham, who believed in demons, were not only more rationalistically inclined than many of those who believe in demons today, but even more than many of those who do not believe in them.
It is important to realize that belief in demons is not inherently irrational. In the context of the ancient world, it was a perfectly reasonable belief; indeed, it can be argued that it was the most reasonable belief:
Suppose a tree suddenly falls over in the forest. If others account for this by saying that somebody invisible pushed it, the explanation probably seems implausible. But consider our explanation: that an unimaginably large number of unimaginably small and invisible particles, working in concert but without any cognitive capacities to coordinate their activities, pulled the tree down. Is that really easier to believe?—especially for someone who knows nothing of the complex theory of gravitational pull by atomic particles? Without thousands of years of recorded data fed through the geniuses who led to modern physics, the simplest explanation is that the tree fell either because it chose to or because someone willed it to do so-an analogy of cause, if you like, to daily life. But if we can’t see anyone or anything making many of the observable things happen, then we must conclude that some possessors of will are invisible. Enter the deities and spirits: invisible possessors of will, who can make things happen out of nowhere… The question is now not “What made the tree fall? but “Who made it fall?” and to answer the latter, one’s entire attention and data-collecting capacities are focused in a different direction. (Elizabeth Wayland Barber and Paul T. Barber, When They Severed Earth From Sky: How the Human Mind Shapes Myth (Princeton University Press 2004) p. 42)
As a result, what has been termed a “towering edifice of authority” was built up to support demonic magic, supported by religion, classical literature, scientific writing, and popular belief. The belief in demons thus cannot be classified as an inherently irrational belief.
We do well to remember that the [pre-modern] world… was a rational world, in many ways more rational than our own. It is true that it was a world of witches and demons… But this was the given reality about which most of the decisions and actions of the age, throughout the entire western world, revolved. (David E. Stannard, The Puritan Way of Death (Oxford University Press 1977) p. 69)
However peculiar they now seem, the beliefs of pre-modern people were normally a rational response to the intellectual and social context in which they were expressed. (Darren Oldridge, Strange Histories, p. 3)
This was not only true of the early medieval period, but even of the seventeenth century:
Delmedigo’s testimonia for these beings are hardly ludicrous when judged by the sensibilities of seventeenth-century Jewish and Christian culture. Moreover, as I have discussed in the case of Abraham Yagel, demonology in this era was more than pseudo-science and superstition. At its best, it represented a rational attempt to explain the unknown and could often contribute to the scientific discourse of the sixteenth and seventeenth centuries. (David Ruderman, Jewish Thought and Scientific Discovery in Early Modern Europe, p. 143)
Thus, instead of categorizing the rabbinic authorities cited in this study as those who believed in demons and those who denied their existence, it would be more meaningful to categorize them as rationalists (which includes many who did believe in demons) versus dogmatists. We should further acknowledge that there is a spectrum of attitudes rather than a clear division between two extremes. The mere fact of someone ultimately accepting that demons exist does not at all mean that he is not a rationalist—it all depends upon the historical context.
Natan Slifkin, Wrestling with Demons: A History of Rabbinic Attitudes to Demons (NP: ZooTorah, 2011), 25-27.