People who identify with the various versions of the skeptic / atheist / rationalist / freethinking movement(s) hold up the Enlightenment, the famous “Age of Reason,” to be the pinnacle of human civilization, as well as a model for future progress. Richard Dawkins famously said that he considers himself a son of the Enlightenment, and my favorite philosopher of all time, David Hume (Aristotle and Bertrand Russell complete my personal pantheon) was a prominent exponent of the Scottish Enlightenment — not to mention the source of the famous Sagan dictum, “Extraordinary claims require extraordinary evidence” (Hume’s version, in An Enquiry Concerning Human Understanding, was “A wise man proportions his belief to the evidence”).

There are good reasons to admire the Enlightenment as a cultural movement. It was a reaction to (and rejection of) centuries of religious wars in Europe, it featured a call for the use of reason and the popular spreading of knowledge (just think of the famous Encyclopédie curated by Denis Diderot and Jean le Rond d’Alembert), and was propelled by some of the foremost intellectual figures of all time (it’s a long list, which includes: Spinoza, Locke, Voltaire, Newton, Rousseau, Montesquieu, Benjamin Franklin, Thomas Jefferson and many others, aside from the above mentioned Hume, Diderot and d’Alembert).

Yet, as John Fleming reminds us in his somewhat idiosyncratic The Dark Side of the Enlightenment: Wizards, Alchemists, and Spiritual Seekers in the Age of Reason, this was also the time of movements like that of the Convulsionists (a religious movement preaching celibacy and the Second Coming), of secret societies like the Rosicruceans and the Freemasons, and occult figures such as the Count Alessandro Cagliostro. So when you proudly declare yourself to be a son of the Enlightenment you should be historically savvy as well as careful in specifying which aspects of the Enlightenment you are referring to.

The point made by Fleming is not simply that during the Enlightenment there were contradictory social forces at play, some progressive (as we might call them), some reactionary. That is true of pretty much any time and place in human history, though perhaps rarely in such a dramatic form as the case at hand. Rather, Fleming is underlining the fact that people like Cagliostro, who dealt in alchemy and other occult practices, thought of himself as doing the same sort of thing that the philosophes were advocating: using reason and science to further knowledge and solve human problems. And let’s not forget, of course, that major thinkers like Newton spent just as much time doing what we recognize as legitimate (indeed, revolutionary!) physics as he did carrying out alchemical experiments or pouring over Biblical texts in search of hidden meanings.

In fact, in an important sense, one can see the Enlightenment as a major bifurcation point in the divergence of (what later we began to think of as) science from pseudoscience. That is the last time I can think of when the contrast between figures like Newton and Cagliostro made sense at all. The equivalent comparison today would be, say, Stephen Hawking and Deepak Chopra (and I’m paying a huge compliment to Chopra by comparing him with Cagliostro!). The two couldn’t be any further apart, with Chopra clearly dealing in snake oil and Hawking who wouldn’t think for a second of wasting time in the pursuit of some of the more occult stuff that Newton was so fascinated by.

I recently wrote about Maarten Boudry’s pseudoscience “black hole” (Steve Novella also commented on it), the idea that once a notion slides into pseudoscientific territory it cannot emerge beyond the event horizon of rationality (to slightly modify Steve’s apt phrase). Perhaps there is such a thing as a well defined historical event horizon, marked by the Enlightenment (and the immediately preceding Scientific Revolution), which began to irreversibly shape our concepts of science and pseudoscience so that physics, biology and the like would definitely belong to the first, while notions such as alchemy, numerology, and so forth definitely fall into the second — with pretty much no hope at this point of any of these fields crossing categories.

This way of looking at things (which is left, unfortunately, largely unexplored by Fleming’s book, as it turns out to be a patchwork of interesting, but ultimately disconnected, mini-biographies of peoples and movements) helps our understanding of the science-pseudoscience demarcation problem. The demarcation line, as is well known, is both fuzzy and changing through time, but is arguably becoming sharper because of scientific progress.

Take biology, for instance. As a proto-scientific field arguably it goes back at least to Aristotle and his field work observing the shapes of mollusk shells on the island of Lesbo. But it was then plagued on and off by a number of quasi- or downright pseudo-scientific notions, all the way up to the natural theology of the early 19th century. Even after the Darwinian revolution, vague notions such as vitalism still reared their ugly heads from time to time, and it is only with the triumphs of genetic first and molecular biology later that biology has come into its own and has pretty much permanently expunged non-mechanistic notions from its research programs. Similar historical paths can be traced for physics and chemistry, of course.

Science didn’t really become recognizably such until the Scientific Revolution of the 17th and 18th centuries, and the process has unfolded at a different pace for different disciplines, with psychology, for instance, coming into its own only during the second part of the 20th century. Indeed, psychology is yet another good example of how the process of becoming a science seems to also imply a sharper definition (and increasingly forceful rejection) of related pseudoscientific notions. Freudian and other types of psychoanalysis — as important as they were at the beginning of the 20th century for the emancipation of psychology from philosophy — are justly considered pseudoscientific nowadays, though a surprising number of practitioners still cling to them. This doesn’t seem to me to be very different from where alchemy and physics were at the time of the Enlightenment.


The bottom line is that human knowledge makes progress in haphazard and patchy ways, at a different pace for different disciplines, and with plenty of gray areas that may literally take centuries to sort themselves out into black and white (or at least less gray). So reading about the history of science and rationality, and especially about the crucial period of the Age of Reason, is not only a way to get a better sense of the struggle, but also provides a humbling lesson in how difficult it is sometimes to sort the wheat from the chaff.

If Newton couldn’t, are you so darn confident that you can?

Originally on Rationally Speaking